Investment Property in London and the UK: Adding Value Through Planning, Conversion and Extension

Why yield alone no longer works for investment property in London

For twenty years, the London model was simple. Buy a let building, collect the rent, and wait for the price to rise. That model has a problem now: London is expensive to enter, and the rent takes a long time to repay the price.

Since borrowing stopped being cheap, the gap has widened. A yield that looked acceptable when money was almost free looks thin against the cost of debt. Serious buyers, family offices and developer-investors have moved on. They buy the building for what it can become.

That shift changes the whole purchase. The question is no longer what the building yields. It is what the building could become, what that will cost, and what it is worth then. That is a development question. The rest of this guide answers it.

The five routes that add value to an investment property

Almost every value-add deal we see in London and the UK uses one of five routes, or combines two of them.

1. Planning uplift on an existing building. The building stays, the consent changes. A new permission for a better use, more units or a bigger envelope can be worth more than any work on site. In England, a full permission must normally be begun within three years of the grant.
2. Commercial-to-residential conversion. Offices, shops and other Class E buildings become flats. Some qualify for commercial to residential conversion under permitted development; others need a full application. The conversion usually changes the value per square foot more than any other route.
3. Extension and infill. A rear extension, a side infill or a new building on a yard or car park adds floor area where the land already exists. The cost is mostly structure and services; the value is the extra saleable area.
4. Airspace and extra storeys. On the right block, the roof is a site. Airspace development and rooftop extensions can add up to two storeys of homes above an eligible building, under permitted development or with a planning consent.
5. Refurbishment and re-letting. The use stays and the building is brought up to the standard tenants now pay for. Our guide to a value-add commercial refurbishment strategy covers this route in detail; this article is about buying to develop.

The routes stack. At Allitsen Road, which we come to below, a conversion, a roof extension and a basement were tested together. The right combination won, not the biggest.

What each route needs: consent, structure, freeholder and cost

Each route comes with its own set of questions. Answer them before you bid, because they decide the price as much as the location does.

Two of these routes have a permitted development path worth knowing in detail.

Conversion under Class MA

A building in Class E use for a continuous two years can change to flats under Class MA, with prior approval from the council. The council looks at transport, contamination, flooding, noise from neighbouring commercial premises, natural light in every habitable room and fire safety. In a conservation area, it also looks at the ground floor.

Since 5 March 2024 there is no floorspace cap and no vacancy test. Listed buildings are excluded, and the work must be completed within three years of the prior approval. Many London boroughs have removed the right with an Article 4 direction, which means a full planning application instead.

Airspace under Class AA

Class AA allows up to two extra storeys of homes on a detached commercial or mixed-use building of three storeys or more. The building must have been built between 1 July 1948 and 5 March 2018.

The roof can rise by no more than 7 metres and the result must stay below 30 metres. Listed buildings and conservation areas are excluded, and prior approval is required.

Whatever the route, the structure and the freeholder decide what the consent is worth. A roof that cannot carry two storeys, or a head lease that forbids the use, turns a consent into a drawing. Before you buy, read our guide to buying land with planning permission for the checks that apply to any consent.

A real example: Allitsen Road, St John's Wood

The building was a former private members' club on the corner of two streets in St John's Wood, in a conservation area. It was vacant and derelict inside. It was bought at auction in 2026 without proper due diligence, against a guide of £2,750,000.

Our Allitsen Road feasibility and design study asked one question: what could 5,038 sq ft of club become? We designed and costed four schemes, from a conversion within the existing building to seven flats using the basement and the roof.

The money was not where the client expected. The biggest scheme, seven flats with an excavated basement, had the highest value. But the excavation added around £240,000 and three months to buy one basement one-bed worth £260,000 to £350,000.

The recommended scheme raised the ground floor instead, making the basement habitable without digging. It delivered 97% of the maximum value at 91% of the maximum cost, with none of the excavation risk.

The planning side moved even more money. A members' club has no automatic route to flats. The council expects sustained evidence that the old use is dead, which the study planned as 12 to 18 months of marketing evidence.

The building's vacancy history could cut the affordable-housing bill by over £1,000,000. So the standing instruction was to leave the empty building alone until the strategy was fixed.

That is what value-add means in practice. The location set the value. The scheme, the planning strategy and the build cost decided how much of it reached the investor.

Investment property for sale in London: where the real opportunities come from

Most buyers start on the portals. Most of the best buildings never get there. A building with real development potential is usually sold before it is marketed, or marketed in a way that hides what it could be.

1. Agents and portals. The widest choice and the most competition. A building listed as an investment is priced on its rent, which hides the development value. Or it carries a "development opportunity" appraisal built for the seller.
2. Auctions. Fast and final. Tired, vacant and part-let buildings go to auction because they are hard to value. The legal pack is published days before the sale, so the checks must be done in that window. Allitsen Road was bought this way, without them.
3. Off-market through live projects. A landowner next to a job, a consultant who knows a consent is about to lapse, a lender with a stalled scheme. Less competition, but all the checking is yours.

We are in the industry and active on projects, so off-market deals come to us. We already have deals on the table. Tell us what you are looking for, and if you want to discuss what we have right now, get in touch.

Whichever route, look for the same signs. Vacant or under-used buildings. Upper floors over shops. Flat roofs on blocks of three storeys or more. Yards and car parks. Streets where the neighbours have already won consent. For sites rather than buildings, our guide to a development site for sale covers the same checks.

The numbers that decide a value-add investment

A yield buyer values a building from its rent. A value-add buyer works back from the finished scheme. The difference between the two is the whole opportunity, and also the whole risk.

Take the sales value of the finished scheme. Take off the build cost, the fees, the finance, the planning obligations and a fair profit. What is left is the most you can pay for the building. Our development appraisal and feasibility study runs this with real costs; the method is in our guide to development appraisal and residual land value.

The illustration below uses made-up round numbers. The finished scheme sells for £9,000,000 and the buyer wants a 20% profit on sales. The only change between the columns is a build cost priced from a rate per square foot, and the same scheme priced by a builder.

A build cost £700,000 higher, plus £100,000 more in fees and finance, cut the price from £2,200,000 to £1,400,000. Pay £2,200,000 on the rate-per-foot figure and the profit has gone before the scaffold goes up.

The four numbers that decide most deals

Four numbers decide most deals, and none of them is the yield.

1. The sales value, tested against real comparables for the finished product, not the asking prices.
2. The build cost, priced by people who build, with the fire strategy, the services and the structure included.
3. The obligations, affordable housing, CIL and Section 106, which can run to seven figures in central London.
4. The finance and the exit, how long the money is out, what it costs, and whether you sell, refinance or hold.

The traps that catch value-add buyers

The traps below have each cost a buyer more than the profit on a deal. All of them can be found before exchange.

1. Vacancy history. It can be worth over £1,000,000 in affordable-housing relief, as at Allitsen Road, and an innocent interim letting can lose it.
2. Listed fabric. A listed building is outside Class MA and Class AA, and every internal change needs listed building consent. The conversion still works, but slower and dearer.
3. Rights of light. Extensions and extra storeys can cut the light to neighbours, who can claim an injunction or damages. Get a rights-of-light survey before you price the extra floors.
4. Article 4 directions. Where the borough has withdrawn the permitted development right, the shortcut is gone and a full application decides the scheme.
5. Service charges and the lease structure. Leaseholders, a head lease or a freeholder with a roof interest can veto an airspace scheme. Read every lease before you value the roof.
6. The auction pack. Days to read it, no second chance. The special conditions and the planning history often carry the cost.

Our development site due diligence checklist lists every check in order. For a conversion, start with the common commercial to residential conversion mistakes.

How we work with value-add investors

We work for the buyer, not the seller, on development schemes from £3M to £150M gross development value, in London and across the UK. Our development land and site sourcing service finds the building or the site, including off-market, and then proves the numbers before you commit. In practice, that means:

• finding the deal that fits your brief, including the ones that never reach the portals;
• running the full appraisal and viability, so the deal works and you make money at the end;
• advising on the chance of planning, or checking the consent and its conditions as your representative;
• highlighting every risk, then negotiating the terms on your behalf.

After the purchase, the same team can take the scheme on through planning, design and construction, as one point of responsibility. Our combined team experience includes £225M+ of land acquired and 10,000+ homes through planning.

Proof of funds, then the checks

We ask serious buyers to have proof of funds, or funding in place, before they approach us. Terms are agreed deal by deal. The checks below are the ones we run first on any investment property with development potential.

An investment property in London or the UK can still make serious money. The money is in the development, not the yield, and it is decided before you buy. Have a building in mind, or want us to find one? Send us your brief and we will show you where the value is first.