Approval in principle (“AIP”) is simply an indication of how much a bank thinks you can borrow.  It is not a legal document and does not entitle you to receive a mortgage loan for the AIP amount.  This stage is only reached when you receive a full final mortgage offer.  You cannot apply for this until you are able to tell the bank the specific property you intend to purchase.   As there can be considerable time lags once you go sale agreed you should immediately contact your bank to convert your AIP to full final mortgage offer.