I managed £15k minus £7k of Scottish government incentives, and I managed to avoid replacing all my radiators by .. getting a "hybrid" system which also includes a boiler for HW :/

Far from ideal solution, but it is mostly green, somewhat offset by the solar panels, and actually more comfortable than the old system because of the more even heating. Set to 20C and forget about it for the season. I'm hoping that it will last until the actual gas phaseout when a solution compatible with 8mm piping will exist.

This is why they need to be mandated on new houses, because it's so much better than trying to retrofit it.