In reply to PTatts:
Any decent estate agent will bat away crap offers. Don't worry about being low, speak to the estate agent, voice your concerns (stamp duty, value of the house, etc). Get an idea on the vendors - ask how quick they can move - if the answer is their packed then go low, if the answer is they're still looking for where to move to, then they won't take a low offer while there is still time.
At the moment estate agents might be busy, but they're facing a potential drop off if the government tries to cool things off.
I put in an offer and got all the negotiating done in 30 minutes four weeks ago. From the estate agents point of view, they want to get deals done quick that won't go sour and move on to the next deal.
Point out that mortgages are getting difficult to get, and especially if you're in a good position, it will be of value.
Our accepted offer is £58,000 below the original asking price. I got £1000 more for my house than I wanted (£4000 below the asking price). Mine was priced to sell, the one I'm buying was priced on an ideal sale.
Research, research, research and then good negotiating skills (basically the exact opposite of anything you've seen on The Apprentice or a used car dealer).