Why is Germany obsessed with this obscure British film?

The 18-minute British sketch has dominated German television every New Year's Eve since 1968, has spawned catchphrases and drinking games, and is almost unheard of in the UK.Miss Sophie has invited her four closest friends for a celebratory dinner, the only problem being that these friends are all long deceased.Before each course, James asks "same procedure as last year?" - to which Miss Sophie replies "same procedure as every year".