Scotland or England? Scots put a house on the market expecting to be offered more, while in England, generally, hoseholders expect to be offered less than the asking price. Apologies to other parts of UK - I've no experience of your systems.
So for Scotland, you add 11 percent over asking, plus a bit more depending on how much you really want it. Mine was "Offers in the region of �280k", I put in �320k, and got it, but heard it was 'tight'.
For england, you work on the 'realistic value', which you can find from numerous free websites which list the selling prices of houses in your area.