This case study is based on a real instruction. Names, addresses and identifying details have been changed, and figures rounded, to protect client confidentiality.

The instruction

We were instructed by a client’s accountant to prepare a retrospective Market Valuation of a purpose-built flat above commercial premises in Wimbledon, SW19, as at 5 April 2015. The property had been sold in July 2026 for £435,000, and the valuation was required to establish the base cost for capital gains tax.

Why 5 April 2015?

That date is the rebasing date for non-resident capital gains tax on UK residential property. Where a non-UK resident disposes of UK residential property, the default position is that only the gain accruing after 5 April 2015 is chargeable, and the property’s market value at that date replaces the original acquisition cost.

Other rebasing and valuation dates come up regularly in our work:

• 31 March 1982 — the general rebasing date for assets held before that date, under section 35 of the Taxation of Chargeable Gains Act 1992.
• 6 April 2019 — rebasing for non-residents disposing of UK non-residential property and certain indirect disposals.
• The date of death — for probate, and as the acquisition cost for beneficiaries.
• The date of a transfer between connected persons, where market value is substituted for actual consideration.

The valuation problem

Valuing at a date eleven years in the past is not a matter of taking today’s value and running an index backwards. Section 272 of TCGA 1992 requires the price the asset might reasonably be expected to fetch on a sale in the open market at that time, which means reconstructing the market as it then stood, using evidence available at that date.

This particular property also had two characteristics pulling in opposite directions:

• A private roof terrace — genuinely rare in this value band. In the local market, flats with meaningful private outside space are typically the larger and higher-value units. A purchaser of this flat was realistically choosing between it and a purpose-built flat at similar money with no outside amenity at all, which supports a positive adjustment.
• A position above commercial premises — which caps the achievable rate per square foot, narrows the buyer pool, restricts lender appetite, and can lengthen the marketing period required to secure market value.

Method

1. Establish the physical facts as at the valuation date. Floor areas, accommodation, building type and specification were taken from the sale particulars and title documents, cross-referenced with the client’s confirmation that no refurbishment or modernisation beyond routine repair had occurred between 2015 and the sale. That confirmation is important: it means the property being valued in 2015 is materially the same property that sold in 2026.
2. Assemble contemporaneous comparable evidence. Completed sales of comparable flats in the immediate area transacting close to April 2015, analysed on a rate per square foot basis, with adjustments for size, floor level, condition, outside space and building type.
3. Adopt a baseline rate and adjust. We adopted a baseline of £620 per sq ft, with +10% for the private roof terrace and −10% for the above-commercial position. On the facts these adjustments substantially offset one another.
4. Cross-check by indexation. We indexed the July 2026 sale price backwards to 5 April 2015 using the Land Registry House Price Index for flats and maisonettes in the London Borough of Merton — the most granular published series available for this property type and location.
5. Reconcile and adopt. The comparable-based figure and the indexed cross-check sat close enough together to give confidence in the result.

The valuation

We adopted a Market Value at 5 April 2015 of £400,000.

The report set out the comparable schedule in full, the analysis and adjustment of each comparable, the reasoning behind the terrace and above-commercial adjustments, the indexation cross-check with its limitations stated, and the assumptions and special assumptions on which the valuation was made. It was prepared in accordance with the RICS Valuation – Global Standards, current edition effective 31 January 2025, together with the UK national supplement.

Why the report needs to show its working

A retrospective valuation is a figure that may be examined by HMRC, and where it is disputed, referred to the Valuation Office Agency. A bare figure on headed paper will not survive that process. What does survive is a report that shows contemporaneous evidence, explains each adjustment, addresses the property’s weaknesses candidly, and is signed by an RICS Registered Valuer prepared to support it.

We say so explicitly in reports of this kind: a valuation that only argues one side is easy to attack. Setting out that the above-commercial position may narrow the buyer pool and lengthen the marketing period is not a concession — it is what makes the rest of the analysis credible.

The tax context

For the 2026/27 tax year, capital gains tax on residential property is charged at 18% on gains falling within the individual’s remaining basic rate band and 24% above it, with an annual exempt amount of £3,000. Where tax is due on a UK residential property disposal, it must be reported and paid within 60 days of completion. A properly evidenced base cost is therefore worth establishing promptly — and it is worth getting right, because on a gain of this size a £30,000 difference in the 2015 value changes the tax by up to £7,200.

We are chartered surveyors, not tax advisers, and we work alongside the client’s accountant rather than in place of them.

Frequently asked questions

Can you value a property at a date in the past?

Yes. A retrospective valuation assesses market value at a specified historic date using evidence that was available at that date — contemporaneous comparable sales, market conditions and the property’s condition at the time. It is a standard piece of RICS Red Book valuation work, commonly required for capital gains tax, probate and litigation.

Why do I need a 5 April 2015 valuation?

5 April 2015 is the rebasing date for non-resident capital gains tax on UK residential property. Where the default rebasing method applies, only the gain accruing after that date is chargeable, so the property’s market value at 5 April 2015 becomes the effective base cost.

Will HMRC accept an estate agent’s appraisal?

An estate agent’s letter is not a valuation and carries little weight if the figure is challenged. HMRC and the Valuation Office Agency expect a formal valuation prepared by an RICS Registered Valuer in accordance with the Red Book, setting out the evidence and reasoning relied upon.

How far back can a retrospective valuation go?

There is no fixed limit. We regularly value at 31 March 1982 for long-held assets. The further back the date, the more the work depends on archived transaction records, historic market commentary and indexation cross-checks, and the more important it is that the methodology is transparent.

Need a valuation at a historic date?

Blakes Chartered Surveyors prepare retrospective Red Book Market Valuations for capital gains tax, probate and litigation, working directly with accountants, solicitors and taxpayers across London and the South East. Roshan Sivapalan BSc (Hons) MRICS is an RICS Registered Valuer with 20 years’ experience. RICS regulated firm no. 752265.

Call 020 7373 7373 or email info@blakessurveyors.com.