Just seen on the news that Thames Water is going to reduce the water pressure in London until they can find the money to replace the leaking water mains. Potential combi owners (and current combi owners) might want to bear this in mind.
One of the London boroughs has had to spend £1M so far on providing booster pumps so water will reach the tops of their taller buildings, and as the pressure drops spread, they are expecting to spend the same again. They have complained to OFFWAT that Thames Water is allowed to drop the pressure but not responsible for picking up the bill. Some taller houses will apparently also need booster pumps.