There are currently 15 lenders offering 144 products charging a percentage fee with the fees ranging from 1% to 2.5% of the mortgage including a number of major high street lenders.
The majority of percentage fees tend to be around 1% of the value of the loan which would mean someone with a £150,000 mortgage paying £1,500. However for a 2.5% fee the bill would rise to £3,750.
Certain lenders give borrowers the chance to choose between fixed and percentage fees depending on their circumstances.
Those looking to take out a two-year fixed deal with Cheltenham & Gloucester at 60 per cent loan to value for example can choose between deals with an interest rate of 2.99 per cent and a fee of 2.5 per cent and an offer charging 4.09% interest and a fee of £995.
Julie Speed, National Accounts Director at Evaluate Technologies said: "Fees have clearly become part of the pricing for mortgages, rather than reflecting the work involved. To charge twice as much for a £200,000 loan as is charged for a £100,000 loan does not seem to be in keeping with Treating Customers Fairly. I am surprised that this is continuing when there have been so many examples of fees being over-ruled as unfair.
"In most cases it's advisable to avoid any loan which comes with a percentage fee attached as anyone borrowing more than £100,000 is unlikely to find themselves better off as a result.
"That said, there are lenders with a flexible approach to charges and in these circumstances it will pay to weigh up the various options."
Amongst those lenders currently charging percentage fees are BM Solutions, Cheltenham & Gloucester, Halifax, Leeds Building Society, Manchester Building Society and Northern Rock on buy-to-let mortgages.
