Provided you have not exchanged contracts you can use the results of the survey to renegotiate the purchase price if the survey reveals any serious issues.
For example, if you have made an offer on a property but the survey reveals that the property has a damp problem, you would get a quote from a damp proofer to correct the problem.
The quote states that it will cost £2000 to correct the damp issue, and you may argue that you where unaware of the problem when you made your original offer. You can ask the current owner to cover these costs (this is usually done through the estate agent) by taking £2000 off the purchase price, or ask them for a contribution towards the work, such as £1000.
Please note that some owners may refuse to agree any contribution and this could mean that the sale falls through.