The Gas Safety (Installation and Use) Regulations 1998
can be found here...
http://www.opsi.gov.uk/si/si1998/19982451.htm
Of interest is the following from PART A GENERAL
(6) Nothing in these Regulations shall apply in relation to
(c) work in relation to a control device on a gas appliance if -
(i) the device is intended primarily for use by a consumer of gas; and
(ii) the work does not involve breaking into a gasway.
Peccavi
July 2009