Our ex-tenant had (and has) a significant job being responsible

Our ex-tenant had (and has) a significant job being responsible for the maintenance of 40 taxis. He is self employed and earns £14.50 per hour, say £2436/month. He became extremely erratic in his rent payments (£430/month) and eventually left without notice leaving the house extremely filthy with two months of rent and water charges unpaid. I found him in his workplace and he told me he is staying with friends. He agreed with me in writing (unwitnessed) that he would surrender his deposit (£430- currently with the DPS) to me and pay off the amounts owing and £70 in respect of the cleaning bill (total £540.24) in three instalments at the ends of May, June and July respectively. However, he says he can't find his DPS Tenant's repayment number and has failed to pay the end-May instalment. He never tells the truth and never keeps to any undertaking he has made. The deposit problem is now with the DPS.What can I do about the rest?