On 10 December 2010, Bates was convicted of three counts of common assault and public disorder, while drunk, having punched a paramedic on 20 January 2010, and was ordered to pay fines, compensation, and costs totalling £5,490. The Welsh Liberal Democrats began proceedings to terminate his membership of the party.

Bates resigned from the party before the Welsh Liberal Democrats could convene a committee of enquiry and served the remaining months of his term of office in the Assembly as an independent. He did not stand for re-election.