Around a third of Britain’s richest people, which includes many property investors, are under tax investigation by HMRC over almost £2bn of potentially underpaid tax, official data suggests.

The inquiries mostly concern avoidance and the legal interpretation of complex tax issues, rather than evasion, according to a report by the National Audit Office (NAO) into the tax authority’s handling of high net worth individuals.

There are currently around 6,000 issues involving super rich individuals – those worth over £10m – under inquiry that have been open for more than 18 months, 4,000 of which have been open for more than three years.

There were around 6,500 people classified as high net worth individuals by HMRC at the start of the current tax year, including many property investors; last year they paid £4.3bn in tax.

Sunday Times Rich List

The property industry’s big players – none of which have been mentioned as being under investigation by HMRC – dominated the top of this year’s Sunday Times Rich List, with the Reuben brothers topping the list for the first time with an estimated wealth of £13.1bn.

David and Simon Reuben, Indian-born brothers whose property portfolio includes the Millbank Tower and dozens of West End properties, saw their wealth rise by £3.4bn over the past 12 months, partly due to “hidden value” in their London portfolio, which has benefited from a surge in values. 

The Duke of Westminster, Gerald Grosvenor, saw his fortune increase by £790m to £9.4bn, moving him up to sixth on the Rich List, up from ninth, thanks in part to a sharp rise in the value of the firm’s investment properties, much of which is located in and around Mayfair and Belgravia.

The Barclay brothers, David and Frederick, the property tycoons who also own Telegraph Media Group, moved up one position to 13th as their fortune increased £500m to £7bn, thanks partly to the sale of stakes in three central London hotels, Claridge’s, the Berkeley and the Connaught, last year.

The Earl Cadogan, Charles Cadogan, was 16th with a £900m rise in his wealth to £5.7bn after sharp rises in capital values and rents on about 200 London properties acquired in 2014.