London home valuations: buyers are paying thousands of pounds too much for homes that don't measure up

London house buyers are paying thousands of pounds too much for their properties because rooms have been badly measured by estate agents, a report claimed today.

A survey of more than 300 flats and houses across the capital found that not one was marketed with figures for overall floor space accurate to within 5sq ft.

In almost a third of examples, the stated size of the property was out by at least five per cent and in one in nine cases there was an error of 10 per cent or more.

Across the entire sample, the average inaccuracy for flats was 32sq ft — equivalent to £20,039 — and for houses it was 92sq ft, worth £57,697.

The report, The Risks And Costs Of Mismeasurement In Residential Property, was written by a team led by University College London PhD researcher Kirthika Mohan.

It concluded: “It’s not really a case of if your property is measured inaccurately but how much, and therefore how much the valuation could be out.” With home valuations in London averaging close to £700-per-sq ft, a small discrepancy could cost a buyer or seller huge sums.

It said errors were introduced by use of old-fashioned technology such as tape measures, human error in adding up room sizes, over-simplified measurements of irregularly shaped rooms, and ignoring spaces such as eaves.

In about 60 per cent of cases, floor sizes in agents’ sales particulars were overstated, meaning that the property was overvalued.

The report was commissioned by property tech company Spec, which uses a high-tech 3D camera to calculate floor space.

Founder of lobby group HomeOwners Alliance Paula Higgins, said: “Estate agents must ensure they provide accurate floorplans and measurements, or they could mislead buyers.”

Mark Hayward, chief executive of estate agency body Propertymark, said that while it was important for measurements to be as accurate as possible, the majority of British buyers bought with their “heart rather than their head”.