"People who target historic buildings are threatening a unique part of the country's heritage, " Ms Heal said.

BBC: Sandhill Park fire: Four jailed for mansion arson attack

Developers often target long-abandoned historic sites believing they can greatly improve the property's value.

WSJ: A Modern Plan for Historic London Market

If recruitment remains on target, then total police strength could hit a historic high by 2004.

BBC: Analysis: Do we have enough police?