part arrears

Tenancy Types and Management

Property let to two guys jointly from 1/4/2007. Month in advance and bond paid on signing on 1/4/2007. The tenants requested that 2 seperate standing orders be set up each for 50% of the rent. At 1/5/2007 nothing paid into bank but one paid 50% in cash. On visiting the property it was noted that the place is a complete discrace (ashtrays kicked over half eaten pizza on the carpets stinking overflowing kitchen bin etc. and the pre pay electric meeter has not been credited). They are both profesional people who's references checked out.

What would be the best way to proceed?