Big business policing tax avoidance. What could go wrong?

Prem Sikka writes in today's Guardian on the perils of hiving off tax avoidance enforcement. 'The government has mobilised the full might of the state to tackle benefit fraud estimated to be around £1.9bn a year, but the same does not apply to tax avoidance/evasion running at between £35bn and £100bn a year', he argues.