All lenders require a basic valuation. They need to know that they are not lending you more than the property is worth, and that if you sell it off you will get at least as much money back as you paid for it. Although this is often referred to as a survey, it is really too superficial to merit this title.
The valuer arrives at a value by comparing the property with similar ones, taking factors such as age, condition and location into account. The valuation also points out any very obvious major faults which could affect the property's value, but is very brief and is not nearly as detailed as a real survey.
The basic valuation is commissioned by your mortgage lender, and is for their benefit, but unfortunately it is you who must pay for it. If the house is valued lower than the purchase price then your mortgage offer may be withdrawn, or offered on the condition that specified work is carried out on it first. If it does reveal that the house is worth less than the price you have agreed to pay for it, you may be able to renegotiate the price, but first double-check with the surveyor how the value given was reached, and that he or she is certain you are paying too much.
The basic valuation takes about half an hour, and costs between around £100 and £300, depending on the price of the house. Some mortgage lenders waive the fee for the basic valuation as part of a package to attract your custom.