The property boom has brought with it a brand new crime - mortgage fraud. It involves estate agents, valuers and solicitors as well as ordinary purchasers, and it's happening both because mortgages are so easily available and because the bodies set up to monitor house sales seem unable to cope with the frantic buying market. Robin Denselow reports from London and Birmingham, where house prices have risen by 50 per cent this year, and where building societies and financial institutions are buying up strings of estate agents. Will the arrival of the powerful new player clean up the property market or just bring new problems?