a letting agent is trying to rip me off.?

I am in the UK - I went to view a flat and gave the letting agent a holding fee last saturday. The flat needs some repair work so the agent promised it would be ready in a couple of days. But it has been a week now. I have asked him for my money back but he has refused. Its stated on the holding deposit receipt that he gave me that my deposit would be refunded if the work wasnt completed within the stated period. how can i get my money back? I need serious legal advise. I paid £200.