[mikegs]

just drive normally without risking a flat battery pack and the range value will creep up.

That depends a bit. If the OP drives like a joyriding teenager it might go down

 

[mikegs]

it’s totally free

That's pretty much the trump card if you're OK with the slight inconvenience.

before the grant is stopped and prices rocket.

Yeah, but probably no.
The feeling is that the grant inflates what installers charge (they want some or all of it for themselves) and also requires a more expensive smart charger.
As EVs become more normal there will be more production and more installers (and more experience), so prices could actually fall. And if you're happy with a dumb charger it could get very cheap.
The unknown is your specific installation - Some houses are just difficult to fit and that can get expensive. Which is another reason to perhaps defer such a project if it's optional because if you get it done now and then move in a year or two it could be money down the drain. (Nice selling point if the new owner is an EV driver, but just now they are a small minority.)