These two videos come from a British TV programme sometime in the early 1980s and the presenter seems to be Ben Elton. It fascinating seeing a Games Workshop shop selling a wide selection of RPGs and not just GWs own products. I think that dates it to pre-1986. The LARP is Treasure Trap, one of the first LARPs in the world (I believe).
Update: Some more info from Wag (who I got the videos off originally) – “The series was a London based show called South of Watford. It is indeed Ben Elton and dates back to 1984. The guy you see on the start of Part 2 is Pete Garner who went on to start the Labyrinth Club in Chistlehurst Caves – at this point he was still a Civil Engineer. If memory serves me right the GW store you see is the original Hammersmith store.”