I would say to all those considering ASHP for UK heating that they should serioulsy consider either the Hitachi Yutaki or the Sanyo CO2 Eco.

Both these units have had extensive R & D and pose the most realistic threat to traditional heating sources (boilers).

The Sanyo, in particular, is currently the only ASHP able to allow DHW storge at 65 C (using heatpump alone) at minus 20 C and has sufficient built in backup/redundancy heating in case everything turns to Rat S**T ! As it comes as a matched package, it's the one least likely to give aggro.

You get what you pay for!!