A Decision in Principle is also known as an 'Agreement in Principle' or a 'Mortgage Promise'.
A mortgage lender will give you this to confirm how much they might lend you, based on the details you give them and their initial checks. It's not a binding or formal mortgage offer but it could help show sellers and agents that you're a serious buyer.
To find out more, take a look at our Agreement in Principle page (opens in a new window).