Also known as a Decision in Principle (DIP). As part of the application process, the lender will ask questions about you and the mortgage you’re applying for. They will carry out a credit check and then they will make a decision about whether they are likely to be able to offer you a loan for the amount you need. The AIP is the document you will receive to confirm this.
Assuming nothing changes and you’re able to provide the correct evidence for everything requested, there should be no nasty surprises later on when we come to submit your application.