I'm surprised the gas board don't do that free of charge.
Gas Board ?!.
lol, a nostalgic trip down memory lane. It's not the 70's
Not sure about the fitting of it, but the mob in the site below seem to have answers to the questions, the actual parts and guidance.
e.g. Who is responsible for replacing or repairing a meter box?
"If you are wondering who is responsible for your gas or electric meter box replacement, you’ve come to the right place. 40 years ago, gas and electric boards owned meter boxes and were responsible for the upkeep of them. Deregulation has changed that, and now it is not the responsibility of gas or energy companies to repair or replace your broken meter box it is in fact, your responsibility as the homeowner".