A Mortgage in Principle is the first step towards getting a mortgage offer. It gives you an indication of how much you’ll be able to borrow from a specific lender. It’s based on what you've said about your situation, your finances, and your credit history at the time of your application. Once the lender has checked your history with Credit Reference Agencies, they’ll make their decision.
You can use a Mortgage in Principle to help you make an offer on a home. Once accepted, you can then progress to a full mortgage application, and if successful, get a mortgage offer. This is official confirmation that a lender will loan you the money for a specific property. Bear in mind that a mortgage offer will be subject to further checks, like a property survey.