The law firm calculates the average length of custodial sentences for tax fraud is now four years one month, up from three years three months the previous year. Tax fraud includes tax evasion, VAT, excise duty and customs duty fraud.

Olga Tocewicz, senior associate at Pinsent Masons, said: ‘HMRC is pushing hard for longer sentences as it clamps down on tax evasion.

‘Even in cases where the prosecution secures a conviction, it may still appeal if it thinks the sentence is not tough enough.

‘HMRC has come under growing political pressure in recent years to prove to the public that it has a workable strategy in place to stamp out evasion. As a result, it has become more dogged in its approach to sentencing.’

Pinsent Masons predicts the average sentence length for tax fraud may be driven even higher by more successful prosecutions, especially once the strict liability offence for offshore tax evasion comes into force in Autumn 2018.

The offence will apply if a UK taxpayer fails to notify HMRC of his or her chargeability to tax, fails to file a return or files an incorrect return in relation to offshore income, assets or activities. The maximum sanction under the new offence is six months' imprisonment.

The UK's criminal law has also been beefed up by the introduction of two new strict liability offences for companies and partnerships which fail to prevent their employees and other associated persons from intentionally facilitating tax evasion.  Whilst it will take a while for prosecutions under these offences to work their way through to court, HMRC has made it clear that it intends to actively investigate companies suspected of having committed these offences.

Tocewicz said: ‘Both individuals and businesses are facing stringent additional new laws for offshore tax evasion later this year, and should anyone be caught out by these rules, they may face an even lengthier sentence.’

Report by Pat Sweet