> Nobody is talking about banning the sale of gas boilers.

Several energy suppliers websites have pages dedicated to this very topic.

The current 2035 target originates in the ministerial Heat and building strategy policy paper (2020):

"Our ambition is to phase out the installation of natural gas boilers beyond 2035."

In the Annex:

Aiming to phase out the installation of new and replacement natural gas boilers from 2035, once costs of low-carbon alternatives have fallen, in line with the natural replacement cycle, including any hydrogen-ready boilers in areas not converting to hydrogen, to ensure that all heating systems used in 2050 are compatible with Net Zero.

Given the energy policy of the UK, which to many engineers makes absolutely no sense at all, it's impossible to predict what will actually come out of the policy sausage factory next.