I dont think combined Heat and Smoke detectors are available in domestic form, but i may be wrong have a look on the Aico website.
I fit Fire Alarm systems into HMO's (Houses of multiple occupancy) i use the Rafiki 2 wire system, the detectors can be set to various settings including combined heat and smoke. In my area the requirement for the Alarm to meet Local Authority and Fire authority requirements, is that detectors in occupied rooms be set to Rate of rise heat, and in communal areas they be set to Smoke, in unoccupied or unused areas (Loft / Cellars etc) set to combined smoke and heat.
Cheers..........Howard