He's alluding to the fact that in the dim & distant past, British Gas was a nationalised company, and as such, had no need to keep trying to sell stuff. When it was privatised, the add flogging the company had the tag line "Tell Sid". Who Sid was, I don't know, but now it is a private company it needs to make a profit, so it sells stuff, same as Sainsbury or Asda sell stuff to make a profit.