ARWadsworth wrote:

Additionally to the above you will need to make quite a large hole in
the inner wall. Gas meter boxes come complete with a tube that
isolates the gas pipe from the cavity. *This is to stop the cavity
filling up with gas in the event of a leak.

The rear outlet is one of two possible ways of routing the pipe. Our box had
a knockout for it with a label saying "Warning, do not remove unless outlet
to be made using special spigot".

The alternative way is to drill a vertical hole through the bottom of the
box frame outside the house wall and route the pipe down through that then
in through a suitably lined hole through the wall. This maintains a
gas-tight seal between the box and the cavity. That's the way National Grid
did ours last year as shown in these photos:

http://www.flickr.com/photos/rawthey/4812837049
http://www.flickr.com/photos/rawthey/4812837053

--
Mike Clarke