Yes, you can, but it's tricky...
The best way to do this is to arm yourself with comparables of properties that have actually SOLD recently (ideally in the last 3 months) at a different figure - then go back to the mortgage company with them and present them as evidence that the valuer may have made a mistake. It is helpful, when the surveyor visits, to have already got some valuations to hand from local estate agents or from similar properties that have recently sold. This should help to ensure you get the correct valuation in the first place.
