What is an "Agreement in Principle"?

An "Agreement in Principle" is a preliminary mortgage offer made by a mortgage lender on the basis of the information which you have provided. The Agreement in Principle will usually be subject to the mortgage lender carrying out a full credit check and verifying information which you have supplied, such as checking out your income via payslips or a letter from your employer, and verifying the value of the property which you are intending to buy.

An Agreement in Principle does not mean that you are tied to that mortgage lender. However it's not a good idea to request an Agreement in Principle unless you are seriously considering accepting their offer. (In theory, there's nothing to stop you getting as many mortgage quotes and Agreements in Principle as you like.)