Similar to the other thread. I get bad condensation in my house, particularly in my bedroom where it stinks. The problem is that the gas meter box is recessed into the wall and by my calculations, the back of it is touching the cavity side of the inner wall meaning that I get a really cold patch on the wall and when there's heat in there the wallpaper goes mouldy and peels. So, I've packed the meter box out with cavity fibreglass insulation slab stuff. I can't see anything wrong in this but wondered what the masses thought?

Not a problem, but your issue is as the wall is so cold. condensation is forming. I would suggest you baton the wall, install "Cellotex" insullation between them, overboard with 12.5mm foil backed plasterboard. You can then either skim plaster or cover with lining paper and paint to choice. I do it successfully for clients all the time. Barry

Instead of insulating behind the gas meter, why not insulate the door? You'll then have a insulated door, air void, inside wall. Hopefully that lot will be equal to a normal wall.

Only issue i could see is if the insulation some how interferes with the meter or has a spark risk.

The wall can't be insulated inside because it's a solid wall then the cavity then the external wall. The box comes through the first wall and touches the cavity side of the inner wall.
The distance between the box door and the meter is very minimal so I packed behind it and sandwiched a piece between the meter and door so we'll see how it goes. I didn't think it'd do harm but it just felt wrong to do it. Anyway why is the box so big? The meter is lost inside it!

the technical term is cold bridging......zilspeed is the expert on it