Tim+ wrote:

I keep hearing folk extolling the virtues of heat-pumps but I was under the
impression that gas was cheaper for equivalent output.

as ever "it varies", but poke some answers into

https://www.kensaheatpumps.com/heat-pump-costs/#cost-calc

The electricity costs for a heatpump will be about 85% of the cost for
mains gas,m but the installation costs are much higher.