We might be speaking, reading and writing in 'English', but there are phrases words and expressions that aren't encountered in America except to identify someone as British. Context seems to be relevant to applicable use also.
  1. SPLENDID: only heard when uttered by Hugh Laurie, or Hugh Grant it could be a requirement to be used by people named Hugh. I've never experienced it IRL
  2. HORRID: Prominently featured in the nursery rhyme "there once was a girl with a curl in the middle of her forehead. When she was good she was very, very good. But when she was bad she was horrid". Beyond this oft repeated ditty of my life (yes, I am a girl with a curl, at my forehead), no
  3. BRILLIANT!:said as an exclamation of that's great, in films and tv shows from across the pond. I hear it mainly in reference to intellectual superiority, often with a clause. 'He's a brilliant doctor with the worst bedside manner'
  4. RUBBISH: ......trash/garbage doesn't compare as favorably but you know, it suits.
  5. GOT: as part of verb construction with the verb TO HAVE, as in have got. I noticed this working through Duolingo where every mom is a mum.
  6. RECKON: to quote Ed Shirin 'I don't reckon that I did it right'. The Brits seem to use it to mean suppose, or guess. Whereas here in the states its permutation is used to mean equalizing/retribution. A great reckoning will come... hopefully, sooner rather than later.