Is quote sufficient for release of Deposit?

Tenancy Deposits

The tenants have left property in a mess. The agent holds the deposit. They said the carpets needs to be replaced with the deposit money. However, the deposit is insufficient to pay for the carpets. I would like the apartment to be re-decorated before fitting carpets. The agents will only release the money for the carpets on production of a receipt. I cannot afford to fit the carpets until the flat is decorated and they say any excess money I shall have to get it from the ex-tenants. What is the law? Can the landlord request money to be released based on a quote? Or should I have to produce a receipt? Should the agent pursue the money from the tenants or should I have to do so?