HMRC has only produced an illustrative breakdown of the tax gap by behaviour for 2007-08 and 2009-10.
The most recent tax gap estimates were published in September 2011 in ‘Measuring Tax Gaps 2011’, which can be found at the following link:
In ‘Measuring Tax Gaps 2011’ HMRC estimated that evasion accounted for around £4 billion (12%) of the 2009-10 total tax gap.
The HMRC publication ‘Protecting Tax Revenues 2009’:
http://webarchive.nationalarchives.gov.uk/20100330144254/http://www.hmrc.gov.uk/pbr2009/protect-tax-revenue-5450.pdf estimated that evasion accounted for around £7 billion (17.5%) of the 2007-08 total tax gap.
HMRC will publish the 2010-11 illustrative breakdown of the tax gap by behaviour in ‘Measuring Tax Gaps 2012’ in October 2012.