Ariel wrote:
I have a very slow gas leak in my house that I simply can't find.

Is any part of the pipe run from the meter to house buried?
Leaks are more common there.

In the US, a call to the gas utility will produce a tech
armed with the latest in "sniffer' equipment in a
surprisingly short time. g

http://www.omniinstruments.co.uk/test/testo.html
Testo 316-1

A bit pricey for one-off job.

Jim