Yes you can tell them to sod off, already did it twice. Had an engineer round to fit one, my house is 1970s so there is a brick enclosure around the area where the gas metre is, with a hinged wooden top on it. I show him this and he says 'No access mate, you will have to take all that brickwork out before I can fit it.'
so I said fine, don't fit it, watch me stay awake at night fretting about it.
They then call me six months later saying they are coming to fit it. Told them they already tried that and there is no 'access'.
'You have to have one by 2020 you know?'
Yeah. Good luck with that.