We did this recently but we were the vendors requesting it. Often vendors will request if they need access to deposit money for another purchase. We had to supply purchasers with bank documents. I would check to see that they can't draw down more on the loan and that the settlement figure (less deposit) is more than enough to cover the mortgage. Oh and if you are going to say no say it quickly I believe from memory you have 28 days and if no response then the funds can be released. I'm no lawyer so it may be best just to follow their advice but just wanted to let you know our experience.