The Gas Safe Register is the register of approved gas engineers administered by Capita on behalf of the government. Capita took over the scheme from CORGI in 2010.
Any work on gas installations must be carried out by approved engineers, who will issue a certificate to show that the work complies with building regulations and is to the required standard.
When selling, your buyer (and their lender) will want to see that any work which has been carried out - for example the installation of a new boiler - has been carried out by a competent person by checking the gas safe certificate. If you are selling and you have lost your certificate, you can contact either CORGI or Capita, depending on the year in which the work was carried out.
If you aren't sure whether the work was carried out in 2009 or 2010, when the schemes cross over, the Gas Safe Register department at Capita should be able to tell you.
Regardless of whether you have a copy of the original installation certificate, a buyer may insist on seeing a more recent inspection or servicing report.