Are you installing an MHRV system? If not, you could go for an exhaust air heat pump to do the DHW. Nibe and Genvex both do them but I am sure that there are others as well.

If you are going for an ASHP then several of the companies are crowing about how their systems have inverter compressors which mean that they don't cycle as much and also don't have such a big starting current. Examples are Mitsubishi, Hitachi, Daikin Altherma. I have been doing quite a bit of research on ASHPs recently but haven't chosen mine yet. One thing I have noticed is that the noise levels vary a lot. The best seem to be in the mid 40 dB, with some of the better known makes in the mid 50's which, as I understand it, is twice as loud.

Sanyo do a system which uses CO2 as the refrigerant and supposedly produces hot water at high temperatures (up to 65C) but it looks expensive to me, ASHP and tank cost about £5,500.

No too far away Andrew, right in the middle of the Orkney mainland half way between Kirkwall and Stromness.

Sorry to say but running heat pumps for hw are not efficient! especially all the time!!
Check the cop at 55 up to 60 c

Maximum sensible heat output from heat pump is around 55C. Above this, most of them seem to effectively use an immersion heater to get higher temperatures.

Minimum usable temperature of a thermal store is around 45C - below this it's hard to get water at 40C out of your taps/shower.

This gives you a headroom of around 10C between your maximum and minimum temperatures. Even with 1400l of store this isn't very much if your peak usage all arrives at the same time, e.g. 4 members of the family all showering within an hour of each other in the morning. This assumes that you can effectively get that 10C uniformly out of the whole tank, which isn't very likely.

Of course, this depends on your expected usage patterns, and may be different if you all like short showers. I like a good shower to wake up, and am planning for two teenagers in 10 years time when the kids get older. For me, a heat pump doesn't make much sense, but I haven't found a good solution yet.