This is an advert, from LOOK-IN (October 1979), promoting the latest addition to the range: Golf Smurf (presumably one for the middle class dads as well).
ITV's LOOK-IN had already realised the benefits of prominently featuring the little blue goons. It's worth remembering that we're still years away from NBC stumbling across Les Schtroumpfs and, with Hanna-Barbera, launching them to Saturday morning glory (in 1981).
The National chain seemed to quietly vanish in the 1980s. A quick bit of Wikipedia finger-work reveals that the chain, actually owned by BP since 1957, was phased-out through the eighties in favour of the stronger BP brand. Individual stations were, presumably, refitted to operate under the BP facia.
It wasn't the end of the Smurfs however: the animated series (shown randomly on ITV in the UK: LWT, for example, used it as a Sunday afternoon schedule filler) led to fresh waves of merchandising and the figurines themselves were sold in other outlets including gift and card emporiums.