Most British homes haven't been built to support AC. Retro-fitting a heatpump for heating is relatively straightforward, as the heating delivery mechanism (pipes to transmit hot water to wall-mounted radiators) is already in place.
Although you could pipe cool water through the radiators, it's an ineffective form of cooling compared to blown-air systems, and retro-fitting a blown-air system is much more costly than a heating-only heat pump.
Although you could pipe cool water through the radiators, it's an ineffective form of cooling compared to blown-air systems, and retro-fitting a blown-air system is much more costly than a heating-only heat pump.