Thank you all for your comments. I am very concerned that my Heat Pump Supplier is providing this unsuitable type of Thermostat. I have asked them why, but have not had a response. I have thought out a simple 'defeat' mechanism for the existing thermostat which consists of a delay timer that has a delay slightly longer than the 'on' cycle time. (the cycle time can be set to 12/hr so the delay can be as short as 6 mins) The delay timer will switch on the heat pump so when the thermostat is more than 1.5 degrees below demanded temperature (on continuously) the HP will be run after 6 mins. Once the thermostat is within the 1.5 degree limit the delay timer will prevent the HP being run at all. To make this practical the thermostat will need to be set 1.5 degrees hotter than is actually required. A crude solution, but it will make more sense till I can fix it properly!
In answer to your comment, ProDave, I agree that Honeywell make no useful reference to the 'feature' but if you look at the Quick Installation Guide under 4, Parameters, you will see listed a setting 2CR which is the cycle rate with no other information about its use! I have spoken to Honeywell who agree this feature exists and cannot be disabled. Helpful Huh!
I am amazed that professional installers appear not to be aware of this issue and that there is no obvious Heat Pump friendly thermostats. If anybody knows of a suitable Programmable, Wireless, 'Dumb' thermostat I would love to know.