You pay your mortgage deposit as part of the home buying process to your solicitor or conveyancer. They will issue you a document called a completion statement which will include all of the fees for their work, any searches and surveys you need to pay for and it will include the fees for your mortgage product if there are any as well as your mortgage deposit. This is usually the step before exchanging contracts and happens between two to four weeks before exchange of contracts. It can be more or less time. Click here to find out more