Spot and Challenge Rent‑Increase Clauses in London Tenancies

Updated Feb 2026 — practical steps for London renters to identify, interpret and challenge CPI‑linked and rent‑review clauses.

Why this matters now

Since the 2025 reforms and rising inflation volatility, many landlords have widened the use of CPI‑linked (CPI or CPI + X) and annual rent‑review clauses to pass costs on to tenants. London renters are seeing more frequent notices and formulaic increases. This guide explains how to spot weak or unlawful drafting, how to calculate increases using the ONS January 2026 figures, how tribunals and advice bodies are treating CPI clauses, and gives ready‑to‑use challenge scripts and model contract redlines.

Practical examples and borough‑specific negotiation tips are included so you can act quickly, keep increases down or defer them where appropriate.

Quick snapshot: what to look for in your tenancy

• Is your tenancy periodic (rolling) or fixed term? A lot of rent‑increases for periodic tenancies follow a statutory route; fixed‑term contracts can only be increased if the contract says so.
• Does the contract include a clear formula (e.g. “The rent will rise by CPI (All Items, UK) +2% each anniversary”)?
• Does the clause specify which ONS series, which month(s) to compare, how to round, and whether there’s a cap or floor?
• Has the landlord given written notice with a clear calculation and the reference ONS data?

If you can answer “no” or “unclear” to any of those, you have grounds to query the increase.

How CPI / CPI+ clauses normally work (and where they go wrong)

Most common forms:

• Simple CPI: “Rent will increase by the annual rate of CPI (All Items, UK) as published by the ONS.”
• CPI + fixed percentage: “CPI (All Items, UK) + 2 percentage points.”
• Market review clause: rent will be reviewed to market level (different legal rules apply).

Where landlords and agents trip up — and where tenants can challenge:

• Ambiguous reference: clause doesn’t say which ONS series (CPI, CPIH, RPI) or which table. Tenants should insist the contract names “CPI (All Items, UK) — ONS table CPIH/BY-month/date” (see model redlines below).
• Missing baseline: not specifying the comparison months (e.g. Jan 2025 vs Jan 2026) leads to disputable calculations.
• Poor rounding rules: landlords using inconsistent rounding or compounding.
• No cap/floor: an open‑ended clause that produces excessive increases can be argued as unfair.
• Failure to provide calculation/evidence: tribunals have favoured tenants where landlords cannot show their workings or the ONS reference.

Using ONS January 2026 data — step by step

You must use the exact ONS series and months the clause requires. If the clause is silent or ambiguous, ask the landlord to state the series and months used and to supply the ONS table link.

Step 1 — Identify the ONS series required by your clause. If unspecified, ask for “CPI (All Items, UK) — ONS monthly series”.

Step 2 — Identify the baseline month named in the clause (e.g. “the CPI recorded for January in the preceding year”). If none is named, request clarification and propose a reasonable baseline (commonly the month 12 months before the review date).

Step 3 — Get the ONS figures. Go to the ONS website and locate the exact table. (If you need help, Citizens Advice and Shelter both publish how‑to guides for reading ONS tables.)

Step 4 — Calculate the percentage change. Example (hypothetical figures):

• Baseline CPI (Jan 2025): 3.0%
• Current CPI (Jan 2026): 4.0%
• Change = 4.0% − 3.0% = 1.0 percentage point increase

If the clause is “CPI + 2%”, apply the change in CPI as reported by ONS then add 2 percentage points. In other words, if the ONS year‑on‑year CPI increase is 4.0%, the rent change = 4.0% + 2.0% = 6.0%.

Step 5 — Apply the increase to your rent and check rounding rules. If your rent is £1,500 PCM and the allowed increase is 6.0%, new rent = £1,590.

Note: Some clauses are ambiguous about whether the landlord must use year‑on‑year percentage change or absolute index levels. Ask for the exact formula in writing.

What advice bodies and tribunals are saying (summary)

• Shelter and Citizens Advice (early 2026 briefings): both emphasise clarity — landlords should name the ONS series, provide a worked example and supply evidence on request. They recommend tenants challenge unclear increases promptly and keep records.
• Tribunals: recent decisions have tended to invalidate or limit increases where the clause did not clearly identify the index or the landlord failed to provide the calculation. Tribunals are particularly unsympathetic to increases that are retroactive or unsupported by documentary evidence.

These trends mean simple challenges — asking for the ONS reference and calculations — are often effective and low‑cost.

How landlords are applying CPI+ clauses in London (market snapshot)

Market reports from Rightmove and Zoopla in late 2025 and early 2026 show differing pressure across boroughs: inner‑London and high‑demand areas still see stronger upward pressure while some outer boroughs show softer rents. Landlords in higher‑demand boroughs are more likely to press CPI+ increases each year; in softer markets, many accept negotiation or staged increases.

If you live in a high‑demand borough it may be harder to resist, but you also have stronger negotiation options if your property is well‑priced and you can offer a longer tenancy. For context on demand patterns and borough attractiveness, see our piece on Top 10 Areas for Young Professionals in London 2025.

Step‑by‑step challenge workflow (practical)

1. Read the clause carefully and identify the exact wording. Copy the relevant paragraph into your notes.
2. Ask the landlord/agent for the full calculation and the ONS source within 7 days. Send this as an email so you have a record. Use the template below.
3. If the landlord fails to reply or the calculation is unclear, send a formal challenge (use the template below), asking them to pause the increase pending resolution.
4. If the landlord insists or applies the increase without evidence, contact Citizens Advice and Shelter for support and consider a formal complaint to the letting agent’s trade body (ARLA/OEA) or to your local council housing advice.
5. If necessary, pursue tribunal or court routes — only after advice; many challenges can be resolved without litigation.

Email template: request for calculation and ONS source (copy/paste)

Subject: Request for CPI calculation & ONS source — [Property address]

Dear [Landlord/Agent],

I refer to your rent increase notice dated [date] and the rent‑review clause in my tenancy. Please can you provide, in writing, the following within 7 days:

1. The exact ONS series and table used (link to ONS page).
2. The baseline month and the comparison month used.
3. The precise calculation (showing index values and percentage applied) and the formula used.
4. Any rounding rules or caps/floors applied.

Please pause any changes to my direct debit or payments until you have supplied this information and we have had an opportunity to review it. Thank you.

Kind regards, [Name]

Formal challenge template (use if unclear or missing data)

Subject: Formal challenge to rent increase — [Property address]

Dear [Landlord/Agent],

I write to formally challenge the rent increase notice dated [date]. The rent‑review clause is unclear because it does not specify the exact ONS series/table and the comparison months and therefore does not permit an objective calculation. Under guidance from Shelter and Citizens Advice, landlords must provide a transparent calculation and the ONS source. Please withdraw or pause the increase until you have provided full evidence. If you do not, I will escalate via Citizens Advice and consider referring the matter to the appropriate dispute forum.

Please respond within 7 days.

Kind regards, [Name]

Model redlines you can propose before signing or when asking to vary a clause

Below are two redlines you can propose. Use the first if you want stronger tenant protections; use the second as a compromise.

Tenant‑protective redline (preferred)

"The Landlord may increase the Rent annually on each anniversary of the Term commencement date. Any increase will be calculated as the percentage change in the annual Consumer Prices Index (CPI) — 'CPI (All Items, UK)' as published by the Office for National Statistics (ONS), comparing the CPI value for the month which is 12 months prior to the anniversary with the CPI value for the most recent month published at the anniversary date. The calculation will be: ([CPI_current] − [CPI_baseline]) / [CPI_baseline] × 100, rounded to one decimal place. The Landlord will add [X.0] percentage points if and only if the clause explicitly states so. The maximum increase in any 12‑month period shall not exceed [5%] (cap); the minimum shall be 0% (floor). The Landlord must provide the ONS link and full workings at least 28 days before the new rent takes effect. The Tenant may request an independent calculation by a mutually agreed expert at the Landlord's cost if the Tenant disputes the calculation."

Fair compromise redline

"Annual rent increases will use the ONS CPI (All Items, UK) year‑on‑year figure for the relevant months. The Landlord shall provide a calculation and the ONS source at least 14 days before the new rent takes effect. Any increase will be capped at [6%] per annum and rounded to the nearest £1."

Note: fill in cap/floor values that you can live with — 3–6% caps are common negotiation starters.

Borough-specific tactics (practical examples)

Note: these are negotiation strategies based on market dynamics and are not a substitute for legal advice.

• Camden / Islington: high demand means landlords may resist deferral. Offer a longer fixed term (e.g., 18 months) at a smaller phased increase (e.g., half the CPI increase now, remainder in 6 months) in exchange for stability.

• Hackney / Southwark: competitive markets but many newer lettings — argue for transparency and the cap. Use Rightmove/Zoopla snapshots showing similar properties to bargain if the increase outpaces local comparables.

• Croydon / Bromley: softer markets — push for immediate negotiation; landlords may accept a zero or small increase to keep a good tenant.

• Tower Hamlets / Westminster: high turnover neighbourhoods — you may have less bargaining power, but you can ask for repairs or improvements (or energy retrofits) in exchange for accepting an increase. For ideas on negotiating improvements, see How Renters Can Use Energy Retrofit Rules to Cut London Rent.

When you mention comparables, use local Rightmove/Zoopla rent snapshots (save screenshots or links) and include them in your correspondence.

When to escalate: Citizens Advice, Shelter, local council and tribunals

• Citizens Advice and Shelter: both offer free guidance and template letters and can help you check whether the landlord followed the correct procedure.
• Local council housing advice: they can provide additional support and, in some boroughs, mediation services.
• Trade bodies: if your agent is a member of ARLA/UKALA, you can make a formal complaint to the regulator.
• First‑tier Tribunal / court: this is a last resort. Tribunals can review the fairness or enforceability of a clause and examine whether the landlord followed the contract and gave appropriate evidence.

Always keep copies of letters, emails, screenshots of listings and ONS pages. If you pay extra because an unclear increase is applied, keep bank statements.

Checklist to reduce or defer increases (copyable)

• Read the rent‑review clause and save it.
• Ask for the ONS series/table and full calculation in writing (7 days).
• Check whether a cap or floor applies; propose a cap if none exists.
• Propose staged increases or a longer tenancy in return for a smaller immediate rise.
• Use local comparables (Rightmove/Zoopla) to argue market position; save screenshots.
• Ask for improvements (repairs, energy retrofits) in exchange for agreeing part of the increase.
• Contact Citizens Advice / Shelter for support and to check next steps.
• Keep records of all correspondence and payments.
• If unresolved, seek formal advice about tribunal or mediation routes.

Practical example (worked through)

Scenario: You pay £1,600 PCM. Your tenancy clause reads: "Annual increase by CPI + 2%." You receive notice for a Feb 2026 increase. Your steps:

1. Ask which ONS series and which months (email template above).
2. Suppose the landlord replies citing "CPI (All Items, UK) comparing Jan 2025 to Jan 2026; CPI = 3.0% (Jan 2025) to 4.5% (Jan 2026)" (example numbers). Change = 1.5%; increase = 1.5% + 2.0% = 3.5%.
3. New rent = £1,600 × 1.035 = £1,656 (rounded as required).
4. If the landlord cannot produce the ONS link or the numbers are wrong or inconsistent with ONS, use the formal challenge template and propose a cap or deferral while you seek advice.

This shows why getting the exact ONS source and workings matters — small differences in index references or baseline months materially change the result.

Final practical tips

• Don’t ignore a rent increase notice: respond, ask questions, and request evidence.
• Use time as leverage: landlords often prefer to avoid disputes and will negotiate if you are organised and reasonable.
• Document everything from the start; evidence wins disputes.
• If you are about to sign a new tenancy, try to negotiate one of the model redlines above — it’s much easier to fix a clause at signing than after it’s used.
• Seek free help early from Citizens Advice or Shelter; they can point you to local resources or affordable legal help.

This guide gives you the tools to spot weak drafting, force transparency, and negotiate or challenge unreasonable increases. Use the templates and redlines, check the ONS January 2026 figures yourself, and keep records — the simplest transparent request (ONS link + workings) will resolve most disputes.

For related reading about neighbourhoods and negotiating on improvements, see Top 10 Areas for Young Professionals in London 2025 and How Renters Can Use Energy Retrofit Rules to Cut London Rent. For privacy and data points landlords may use when setting rents, see Privacy & AI Checks When Renting in London: A Renter's Guide.

Disclaimer: This article is guidance only and does not constitute legal advice. If you need binding legal advice about a tenancy dispute, consult a qualified solicitor or your local citizens advice service.