And he was great as Trevor. Possibly their most accurate collective impression. With the possible exception of Richard and Judy. Very well known, actually...
Impression shows will always date more than other Christmas specials, because they're usually a snapshot of a very specific period. 90% of the humour requires at least a little knowledge of the context of each sketch. Like all the Ulrika "jokes" in the Beckham's sketch. Add to that, basing entire sketches around specific soap opera storylines that not everyone would have been aware of at the time, let alone 20+ years later, and this special has aged like already sour milk. For me, impressionists always work better in a stand up scenario, cos that's where an impression has to stand up on its own merit, without the safety net of make-up, costumes, sets making it obvious who an impression is supposed to be.
Why aren't comedies and impression shows as funny as this now? There were no politics or resorting to cheap jokes about Tories, Trump, like every BBC comedian these days. They didn't need to do anything deemed "offensive", like the sketches of Little Britain. Just silly, funny jokes, impressions, word play.