Serious tax evasion cases identified by HMRC have fallen by almost a quarter in the past year, according to law firm Pinsent Masons.

In 2011/12 there were 3,456 suspected serious tax evasion cases - involving sums over £50,000 - identified by local HMRC offices, down 23% on the 4,506 cases in the previous year.

The figure represents the lowest number of serious tax evasion cases identified by HMRC over the last five years.

It says that the fall is unlikely to be because HMRC is either becoming less active or less effective in its pursuit of tax evasion.

Pinsent Masons found that HMRC has stepped up its offensive against tax crime by more than doubling the number of property raids it undertakes from 196 in the 2010/11 tax year, to 499 in 2011/12.

Phil Berwick, director at Pinsent Masons, said HMRC is becoming more draconian in its punishment of offenders it successfully identifies. Earlier this year, HMRC pursued criminal action against Melvyn Careswell, a Surrey plumber who evaded £50,000 of income tax.

Berwick said: 'The Melvyn Careswell case is a perfect example of HMRC's current attitude to the prosecution of tax evasion cases. A few years ago, a £50,000 tax evasion case would almost certainly have been subject to civil, rather than criminal prosecution.'

'HMRC is now prepared to use its strongest anti-evasion measures in cases that would previously have been regarded as quite modest in size.'

Only last week, HMRC launched its latest hunt for tax dodgers - London's legal profession.

The legal eagles are among five high-risk sectors being tackled across the UK by specialist task forces that plan to net £19.5m from their tax probes. The teams typically focus on groups of up to 300 in each sector, and examine records and carry out other investigations.

HMRC says it expects its latest assault on non-payers to recover more than £19.5m. Other sectors set to feel the wrath of the taxman's latest probe include grocery and retail outlets in Wales, the North West and the South West; hair and beauty in the north east; restaurants in the south east and Solent and the motor trade in Scotland.

Two years ago, a campaign that examined evasion among doctors and dentists raised £10m for the Treasury's coffers from voluntary disclosures, and a further £3.1m from additional probes using information acquired from insurance companies and elsewhere.

Since May 2011, HMRC has launched 30 taskforces focused on groups including electricians, private tutors and e-traders which are expected to raise a total of £50m.