Landlord not returning security deposit.?

what is to stop him from now saying "Well - the cooker is broken or this, that and the other is broken" - which it isnt. We`ve handed the keys back in now to the agent - all she said was the cupboards were dirty - which they were not! He`s got 700 quid of our money - i understand he`s got thirty days to give it back - that will be up next week.. shall i wait till after the 30 days and then get a solicitor involved? Will this cost us much?