When your solicitor completes your purchase they are required to register you as the new owner at the land registry.  If you have taken out a mortgage details of this are also registered.  Importantly the price you paid is always registered.

The information held by the land registry is open to the public so anyone can obtain details of who owns your property and the price paid on payment of a small fee.

The land registry also licenses the information to various websites.

Their websites are useful tools to enable you to research current prices in a particular locality.  If you are thinking of making an offer on a property.

A few of the websites which supply information on prices are www.property.aol.zoopla.co.uk and www.nethouseprices.com