Fraud linked to the outsourcing of local authority services could soar under government plans to open up public service provision, the sector's largest trade union has claimed.

The government estimates that procurement fraud costs the public sector £2.4bn annually. If such fraud is split evenly across public procurement activities, Unison claimed, local government would account for £470m, central government £825m and fraud linked to outsourced activities would be £1.3bn.