Just copied this from Wiki
The character of Mrs Merton had previously appeared for four years in her own spoof chat show, The Mrs Merton Show. In it, she very often mentioned "my son Malcolm" but he never made an appearance. His screen debut occurred in some advertisements for British Gas,[4] which were the direct forerunner of the sitcom.
I seem to recall some else had 2 answers the same and most people agreed they were correct. Your other answer for Sid sounds right although the answer for that could be British Gas Shares as that is what that ad was about.