Guide · 21 October 2026

Building costs and house prices in City of London

The Square Mile is London’s smallest local authority area and, for anyone thinking about building work at home, its oddest. The Census 2021 accommodation-type table (TS044, via Nomis) counted just 4,914 households in the City of London, and 87.0% of them lived in a purpose-built block of flats, against 40.3% across London. Another 5.5% lived in a converted building such as a former warehouse or school, and 4.1% in a commercial building, for example a flat above offices or shops. Only around 100 households, about 2%, had a whole house: 78 in terraces, 15 in semis and 7 in detached houses.

So the usual London question, extend or move, mostly doesn’t arise here. There are very few gardens to build into and almost no lofts to convert. The building work City residents actually do is inside the flat: a new kitchen or bathroom, taking out or putting in a partition, rewiring, new floors. And much of the City’s housing sits in two listed post-war estates, the Barbican and Golden Lane, where even those jobs can need formal consent.

City of London house prices in July 2026

The latest UK House Price Index from HM Land Registry and the ONS covers July 2026 (provisional). It puts the City’s average price at £710,652, the sixth highest of London’s 33 local authority areas. That is 17.4% lower than a year earlier, the second-steepest annual fall in London after Westminster (−20.7%), although it is 1.7% up on June. The London average fell 3.3% over the same year, to £550,037. The City’s highest month on record in the HPI was January 2022, at £1,021,539, so the average now stands about 30% below that peak.

The HPI doesn’t publish detached, semi-detached or terraced prices for the City at all, because there are too few house sales to measure. The figure that matters is the flat average, which is the third highest in London after Kensington and Chelsea and Westminster, and higher than the average price of a London terraced house.

Treat the City’s numbers with more caution than any other borough’s. The HPI recorded just 6 sales in May 2026, the latest month with a count, and 14 in July 2025. With so few transactions, one or two unusual sales can swing the average by tens of thousands of pounds from month to month, which is part of why the annual fall looks so steep. All figures come from the HPI full data file for July 2026; they are area-wide averages, they will be revised, and they can’t value any particular flat.

Moving or improving?

In most boroughs this guide compares the price gap between property types with the cost of an extension. In the City that sum doesn’t work: there is no official City figure for houses, and the HPI doesn’t split flat prices by the number of bedrooms, so there is no published figure for what an extra bedroom is worth here. We won’t guess one. If you are weighing a bigger flat against improving the one you have, the honest comparison is the asking prices of real flats in your block or estate against real quotes for your own work, plus stamp duty, fees and removals on the move side.

What we can give is a sense of what the work itself tends to cost. Nobody publishes refurbishment costs for the City, so the figures below are UK ballparks from Checkatrade, whose estimators are members of RICS and the CIOB:

• £15,000–£18,000 for a basic flat refurbishment (new kitchen, flooring, decorating, joinery and changes to the existing bathroom), and £33,000–£48,000 for a full one that adds a new bathroom, boiler and radiators, rewiring, replastering and structural work, according to the flat refurbishment cost guide (September 2026)
• £6,200–£16,800 for a budget kitchen renovation and £15,000–£50,000 for a bespoke one, from the kitchen renovation guide (October 2026)
• £1,500–£7,500 for a bathroom remodel, around £4,500 on average, from the bathroom renovation guide (May 2026)

These are national figures, not City quotes. Working in a tower or a deep-plan block in the Square Mile brings its own costs: booking lifts and loading bays, protecting common parts, restricted working hours set by the building, and getting materials in where there’s nowhere to park. Ask each builder to price those separately so you can compare like with like.

Planning rules for flats

Householder permitted development rights belong to houses, and the City Corporation’s planning permission page makes the point directly: most City residents live in flats, and works that would be permitted development on a house may not be on a flat. It adds that even minor alterations such as replacing a window or an external door may need planning permission. The Planning Portal’s guide to flats and maisonettes explains the national position. Purely internal work in an unlisted flat usually doesn’t need planning permission, but it can still need building regulations approval, and anything that touches the outside of the building should be checked first.

If you own your flat on a lease, which almost every City flat owner does, the lease will usually say what you can alter and whether you need the freeholder’s or landlord’s consent first. GOV.UK’s leasehold guide covers the basics. Read the lease before you pay for drawings, not after.

The Barbican and Golden Lane: listed homes

The Barbican Estate is listed at Grade II, and that listing covers the inside of the flats as well as the outside. The City Corporation’s listed building guide for Barbican residents says you will need listed building consent to remove or alter internal walls and partitions, including sliding doors and screens, and to put up a new partition. The original staircase in a maisonette is unlikely to be allowed to go or move, though it may be possible to modify it with consent. Enclosing a roof terrace or adding a satellite dish would normally be resisted. Doing work that affects a listed building’s special interest without consent is a criminal offence, so this isn’t a formality.

The Barbican Estate Listed Building Management Guidelines set out in detail which works need consent and which are likely to be approved. Separately, as landlord, the City Corporation requires an application for Landlord’s Approval before home improvements, with drawings, the contractor’s details and a copy of their waste carrier licence. If you have just bought, the Barbican Estate Office says not to apply until the transfer has been registered with its legal department.

The Golden Lane Estate, built between 1953 and 1962 by Chamberlin, Powell and Bon and home to more than 500 flats, was listed in 1997: the estate and its landscaping at Grade II, and Crescent House at Grade II*. It has its own management guidelines, and the same rule applies: check before you change anything, inside or out.

Tall buildings and building control

Many City flats are in blocks that count as higher-risk buildings: at least 18 metres or seven storeys tall with at least two homes. Since 1 October 2023 the Building Safety Regulator has been the building control authority for those blocks. The Barbican home improvements page notes that applications which would once have gone to City of London Building Control, such as a building notice or regularisation, now go to the regulator instead. Make sure your builder knows which route applies before work starts, because it affects timescales.

Conservation areas, heritage and the new City Plan

According to the City Corporation’s historic environment page, the Square Mile has more than 600 listed buildings, 28 conservation areas, 48 scheduled ancient monuments and four historic parks and gardens. Each conservation area has, or is due to have, a character summary and management strategy explaining what the Corporation wants to protect. If your building is in one, expect closer scrutiny of anything visible from outside, from windows to rooftop plant.

One City-wide Article 4 direction is worth knowing about if you are buying into a conversion: since 1 August 2022, turning offices into homes anywhere in the City has needed full planning permission rather than the national prior approval route.

The planning rules themselves are about to change. The City Plan 2040 will replace the Local Plan 2015 once adopted, and the inspectors’ report, published on 14 October 2026, found it sound subject to main modifications. Until it is formally adopted, check which policies the Corporation is applying to your application.

Party walls in a block of flats

The Party Wall etc. Act 1996 isn’t only about terraced houses. It also covers the walls and floors that separate flats, which the Act calls party structures. Cutting into one to fix a steel, for example, can mean serving notice on the neighbours beside, above or below you. GOV.UK’s guidance explains the notices, the time limits and what happens if a neighbour dissents. In a block, talk to your managing agent early as well; many have their own rules on noise, hours and notice to neighbours.

Checking a builder

Be wary of anyone who offers to start next week without asking about your lease or the building’s rules, wants a large cash deposit, or gives a single round figure with no breakdown. A reliable firm will put the job in writing, link payments to stages of finished work, show insurance and recent projects you can see, and tell you who will deal with building control. In the Barbican or Golden Lane, ask whether they have worked on a listed flat before and how they handled the consents.

You can find registered tradespeople on TrustMark, work through Citizens Advice’s pre-work checklist, and report a rogue trader to your local Trading Standards office.

Figures change: get quotes before you decide

Prices here are UK HPI averages for July 2026; they are provisional, the City’s rest on a handful of sales, and the August 2026 figures are due on 21 October 2026. Refurbishment costs are Checkatrade’s UK figures from May to October 2026, not City quotes. Household figures are from Census 2021. Planning and listed building details come from the City of London Corporation’s pages as they stood when we checked them, and the City Plan 2040 could change them once adopted. Check the rules and your lease for your own flat, and get at least three itemised quotes before you decide whether to improve or move.

Sources: UK House Price Index England: July 2026 (GOV.UK); UK HPI data downloads, July 2026 (full file, City of London E09000001); Census 2021 TS044 accommodation type (Nomis); Checkatrade: flat refurbishment costs; Checkatrade: kitchen renovation costs; Checkatrade: bathroom renovation costs; City of London: planning permission; Planning Portal: flats and maisonettes; GOV.UK: leasehold property; Barbican Estate: a listed building guide for residents; Barbican Estate Listed Building Management Guidelines; Barbican Estate home improvements; Golden Lane Estate Listed Building Management Guidelines; Building Safety Regulator; City of London: historic environment; City of London: conservation areas; City of London: listed buildings; City of London: change of use; City Plan 2040 examination; GOV.UK: Party Wall etc. Act guidance; TrustMark; Citizens Advice: before building work; GOV.UK: find local Trading Standards. Data checked 21 October 2026.