Before you purchase this piano, you should consider hiring a piano rebuilder who has experience with historic instruments to evaluate the instrument's condition. The price sounds a little too good to be true, and if the piano has hidden problems you could be left with little more than an expensive conversation piece. Since you quoted the price in pounds sterling, I'm assuming that you live somewhere in the U.K. You should contact David Winston of Period Pianos (
www.periodpiano.com) for his advice. He has almost thirty years experience with 18th and 19th century pianos and has rebuilt Beethoven's Broadwood and the 1855 Erard that Emanuel Ax used to record the Chopin piano concertos. If he is not available to examine the instrument, he should be able to refer you to another capable rebuilder. The money would be well spent, whether to avoid a bad purchase or for peace of mind.
If funds allow, you might want to consider buying a modern replica of an historic piano instead. Winston, for example, builds a beautiful piano after Brodman that Olga Tverskaya has used in her recordings for Opus 111. With a modern builder you would be assured a quality instrument and continuing technical support. Hope this helps