https://boilerspot.co.uk/combi-boilers.php

Air Source Heat Pumps (ASHP) are generally considered to be a more energy efficient option to gas boilers. By extracting warmth from the surrounding air, the heat energy released can be many times the energy required to power the equipment. In some instances however, a gas-fired condensing boiler may be a better choice, as ASHP systems are, by their very nature, dependent on the ambient temperature and more efficient at certain times of the year.

I've been looking at the area of domestic CHP boilers with interest and I'm now in the market to possibly by one.

Now the technology is not that new, in fact it's 100 years old but that's another matter. Anyway, two companies have been developing them... BG group and Whispergen (being sold through Powergen)