Community Infrastructure Levy in London: The Complete 2026 Guide
How the Community Infrastructure Levy works in London in 2026 — which developments trigger CIL, Mayoral vs borough charges, self-build and householder exemptions, and how to claim them.
The Community Infrastructure Levy is one of the most misunderstood costs in London residential development. Unlike planning fees, it is not a charge for the decision on your application — it is a charge on the floorspace you create, and it can run to tens of thousands of pounds even on a modest new house. Worse, many of the reliefs that would wipe out that bill are conditional on procedural steps that must happen before you break ground.
This guide explains, in plain terms, what CIL is, which London projects trigger it, how the Mayoral and borough charges stack, and — most importantly — how homeowners and self-builders claim the exemptions they are entitled to without tripping over the deadlines. It is written for London homeowners commissioning extensions, loft conversions, and new-build homes across the capital's 33 planning authorities.
What is the Community Infrastructure Levy?
The Community Infrastructure Levy (CIL) is a charge that local planning authorities in England and Wales can place on new development to help pay for the infrastructure needed to support growth — schools, transport, open space, health facilities, and flood defences. It was introduced under the Planning Act 2008 and is governed by the CIL Regulations 2010 (as amended). A charging authority sets its own rates in a published Charging Schedule, expressed in pounds per square metre of new floorspace, indexed to construction costs each year.
Crucially, CIL is a formula-based, largely non-negotiable charge. Once a council has adopted a Charging Schedule, the levy is calculated mechanically from the net additional floorspace your scheme creates. There is very little discretion: either your development is liable and the maths applies, or it qualifies for a specific exemption or relief. This is different from Section 106 planning obligations, which are negotiated site-by-site and secure things such as affordable housing contributions.
Not every London borough charges CIL, and rates vary widely between and within boroughs, often by zone and by land use. Some charge a high rate for residential development in high-value areas and a nil rate in others. Always check the current adopted Charging Schedule for the specific council and the specific part of the borough your site sits in before assuming a figure.
Which London developments trigger CIL?
CIL liability is driven by the amount of new floorspace and by whether a new dwelling is created. As a general rule, a development becomes potentially liable when it creates one or more new dwellings, or when it adds more than 100 square metres of gross internal area (GIA) of new build. Either limb can trigger it: a new house of just 70 square metres is still liable because it creates a dwelling, even though it is under the 100sqm threshold.
Existing floorspace that has been in lawful use for a continuous period can usually be deducted from the calculation, so a scheme that demolishes and rebuilds may pay CIL only on the net increase. This is why an accurate measured record of what already exists — and evidence of its lawful use — matters so much to the final bill.
Extensions and loft conversions
Householder extensions are the most common source of confusion. An extension of 100 square metres GIA or less, to a building that is your existing home and will remain in residential use, is exempt — but the exemption is not automatic. You must submit the residential extension exemption claim and have it acknowledged before you start on site. Most single-storey and modest two-storey London extensions fall comfortably under 100sqm, but larger rear-and-side wrap extensions and full-width double-storey additions can exceed it, at which point the excess becomes chargeable unless another relief applies.
Loft conversions frequently add floorspace without adding footprint. Because CIL counts gross internal area across all storeys, a large loft conversion combined with a rear extension can quietly cross the 100sqm line even where each element looks small on its own.
New dwellings and larger schemes
Any scheme that creates a new, separate dwelling — a new-build house, a garden annexe that is a self-contained unit, or a conversion of a house into flats — is potentially liable regardless of size. For new-build homes and multi-unit schemes the levy is calculated on the full new floorspace less any lawful existing floorspace demolished. On a new London house this can be a substantial sum, which is why self-build relief (covered below) is so valuable and so easy to lose.
How do the Mayoral CIL and borough CIL work together?
Greater London is unusual because it has two tiers of CIL. The Mayor of London is a charging authority in his own right and levies the Mayoral CIL (often called MCIL) across all 33 London boroughs to help fund strategic transport infrastructure — originally Crossrail (the Elizabeth line), with the current MCIL2 schedule continuing to raise funds toward strategic transport including reserves earmarked for Crossrail 2. On top of that, each individual borough may levy its own local CIL to fund borough-level infrastructure.
That means a single London development can attract two separate CIL charges: the Mayoral charge, set by the Greater London Authority and applied consistently across the capital by zone, and the borough charge, set by your local council. They are calculated separately, appear as separate lines, and are collected by the borough on the Mayor's behalf. When you budget for a London scheme, you must account for both, not just the borough figure, and you should check the current Mayoral rate band that applies to your borough.
What exemptions and reliefs can homeowners claim?
The CIL Regulations provide several reliefs that matter enormously to London homeowners. The two most relevant are the residential extension exemption and self-build housing exemption. There are also reliefs for social housing and for charitable development, and a general minor development threshold that keeps very small works outside the levy.
Each relief follows the same non-negotiable procedural spine: you must assume liability, submit the correct claim form, receive an acknowledgement from the collecting authority, and — critically — not commence development until that acknowledgement is in place. Get the sequence wrong and the relief is lost.
Self-build exemption for a new home
If you are building a new house that you will occupy as your principal residence, you can claim the self-build housing exemption, which removes CIL liability entirely on the dwelling. To keep it you must own the property and live in it as your main home for at least three years after completion. The claim requires you to assume liability, submit the self-build exemption claim before commencement, and then, within six months of completing the dwelling, submit further evidence (such as proof of the completion date, a mortgage or title document, and a council tax bill or utility record) to confirm you have taken up residence. Miss that follow-up evidence window and the exemption can be clawed back.
Householder extension exemption
For an extension to your own home of 100sqm or less that does not create a new dwelling, the residential extension exemption applies. You submit the relevant claim before starting work and wait for acknowledgement. Because this exemption is straightforward and common, it is also the one most often lost through impatience — homeowners who begin demolition or groundworks before the paperwork is acknowledged forfeit the relief.
What forms and timings does CIL involve?
CIL runs on a defined sequence of forms tied to your planning permission. In outline, the collecting authority issues a Liability Notice setting out the calculated charge once permission is granted. Before you start on site, someone must submit an Assumption of Liability so the authority knows who will pay, any exemption or relief claim must be made and acknowledged, and a Commencement Notice must be served stating the date development will begin. Once work starts, the authority issues a Demand Notice with the amount due and the payment date, and payment may be phased in instalments where the authority operates an instalment policy for larger sums.
The order is everything. Exemptions must be claimed and acknowledged, and a Commencement Notice served, before development commences. Failing to serve a valid Commencement Notice, or starting early, is what triggers the harshest consequences — even where you would otherwise have paid nothing.
- Assumption of Liability — filed before commencement to nominate who pays.
- Exemption/relief claim — submitted and acknowledged before any work starts.
- Commencement Notice — served before development begins, stating the start date.
- Liability Notice — issued by the authority setting out the calculated charge.
- Demand Notice — issued once development starts, showing the amount and due date.
What are the penalties for getting CIL wrong?
CIL enforcement is deliberately strict because the levy is formula-based and self-declared. If you do not assume liability, the charge defaults to the landowner. If you fail to serve a valid Commencement Notice before starting, you can lose the right to pay by instalments and the full amount can fall due immediately, and any exemption or relief you would have qualified for can be withdrawn — meaning a scheme that should have been zero-rated suddenly owes the full levy. Surcharges can be added for a range of failures, including failing to assume liability, failing to notify commencement, and failing to respond to information requests.
Authorities also have recovery powers, including CIL stop notices that halt work until payment, and ultimately charges over the land. The practical lesson is simple: treat CIL as a pre-commencement discipline, not an afterthought. The paperwork is not difficult, but it is unforgiving on timing, and the cheapest way to handle CIL is to handle it before a single brick is laid.
| Feature | Mayoral CIL (MCIL2) | Borough CIL |
|---|---|---|
| Charging authority | Greater London Authority (the Mayor) | Your individual London borough |
| Coverage | All 33 London boroughs, banded by zone | Only where the borough has adopted a schedule |
| Purpose | Strategic transport (Elizabeth line; Crossrail 2 reserves) | Local borough infrastructure — schools, parks, roads |
| Rate basis | Set per square metre by GLA zone band | Set per square metre by the borough, often by area and use |
| Collected by | The borough, on the Mayor's behalf | The borough directly |
| Applies together? | Yes — can be charged on the same scheme | Yes — stacks on top of the Mayoral charge |
Related services: Planning Permission, New Build Drawings, Planning Drawings.
Frequently asked questions
Does every London borough charge CIL?+
Will my house extension have to pay CIL?+
How is CIL actually calculated?+
What is the difference between CIL and Section 106?+
Can I still claim self-build exemption if I have already started building?+
How long do self-builders have to keep the property to keep the exemption?+
Who is liable to pay CIL if nobody assumes liability?+
Does converting a house into flats trigger CIL?+
When do I actually have to pay the CIL bill?+
Do the drawings I submit affect my CIL bill?+
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