HM Revenue & Customs (HMRC) is creating a new unit to handle the tax affairs of the richest taxpayers as it steps up its drive against tax evasion.

The unit will target high-net-worth individuals, particularly non-domiciles and multimillionaires, and will scrutinise their tax returns to ensure that all income is declared. However, the Revenue says that any wealthy taxpayer with complex tax affairs could come under the spotlight of the unit.

The announcement came as new research showed that HMRC collected 13 per cent more tax from compliance work in 2007-08 than in the previous tax year. UHY Hacker Young, the accounting group, says that extra tax from tax inquiries and interventions rose from £11.4 billion to £12.9 billion. In some fields, the rise was still more marked, with HMRC pulling in 44 per cent more corporation tax from compliance activity targeting big businesses, up from £2.7 billion to £3.9 billion.

HMRC has given businesses some respite in recent weeks, after setting up a Business Payment Support Service in November to let businesses make tax payments over a longer period. More than 20,000 businesses have delayed paying £350 million of tax after contacting the service in the past six weeks.

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However, HMRC aims to collect an additional £7 billion in tax over the next three years, as the Government faces a growing “black hole” in tax revenues because of the economic downturn.

Angela Beech, of Blick Rothenburg, the accountant, said: “The high-net-worth unit will not just target celebrities and those on the rich list - City fat cats with large bonuses or those who have recently sold a business worth millions may also be included. The team will be poring over the details of individual tax returns, checking for any type of undisclosed income - particularly the sale of assets such as property and cars, or very complex investments.”

Ms Beech says that non-domiciled people living and working in the UK will be scrutinised by the Revenue. Non-doms do not pay income tax, capital gains tax or inheritance tax on assets outside Britain, but must pay a levy of £30,000 a year to continue that arrangement after seven years' residence. Non-doms must earn £80,000, at least, to make the arrangement worthwhile.

Ms Beech said: “The Revenue is still very keen to crack down on undeclared offshore income, so I would expect to see a lot of non-doms transferred to this unit.”

The Revenue can investigate any of the millions of self-assessment returns that it receives. Last year it looked into the affairs of 62,100 people, but this year the total is expected to soar.

Investigations can be laborious for the taxpayer. If mistakes are found, the taxpayer must pay the tax owed, plus interest and a penalty of up to 100 per cent of tax underpaid. If HMRC believes that a taxpayer knowingly committed fraud, it can prosecute.

Roy Maugham, of UHY Hacker Young, said: “While the Government's conventional tax take is falling short, it definitely seems to be trying to compensate for this by squeezing more money out of tax investigations.

“This aggressive approach is likely to harden further as pressure mounts on HMRC to prop up falling tax revenues during the downturn.”

Paul Aplin, of the Institute of Chartered Accountants in England and Wales, said: “The Revenue is focusing on a risk-based approach to tax collection, and of course very wealthy individuals with particularly complex tax affairs are the most likely to make mistakes or omissions on their tax returns.”

HMRC said: “The new high-net-worth unit will ensure an integrated and consistent approach to this customer group. All customers and agents affected by this restructuring will be contacted directly to let them know about the new arrangements.”