Benefit fraud and tax evasion

Benefit fraud accounted for £1.2bn of the welfare bill in 2013/14 (0.7% of the entire welfare expenditure):
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/371459/Statistical_Release.pdf

Tax evasion accounted for £34bn of lost revenue in 2012/13 (6.8% of the expected tax revenue):
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/364009/4382_Measuring_Tax_Gaps_2014_IW_v4B_accessible_20141014.pdf