A mortgage product fee is a charge some lenders apply to a specific mortgage deal, usually to secure a particular interest rate or product feature. It is separate from valuation, legal and broker costs, and is sometimes called an arrangement fee or booking fee depending on the lender.
You can often choose to pay the product fee upfront or add it to the loan, though adding it means you pay interest on it over the mortgage term. When comparing deals, look at the overall cost including the fee rather than the headline rate alone, because a lower rate with a high product fee can work out more expensive on a smaller loan. A mortgage adviser can help you weigh the fee against the rate for your circumstances.