I would like to claim that I have completed this, but that would be a little embarrassing. Although I have a full grid and the sixth component, I cannot solve any of the 5 thematic clues nor parse 21a,35a,41a,5d and 17d.
35a def.1st 2 words, usual abbreviation for excellent inside unusual term for strong positions. 17d def. Is last 2 words, a word for a forecaster round A. Still working on the others.
Gitto, I too have a full grid, and the sixth compnent - and I feel a sense of triumph not to have to solve the thematic clues! I didn't parse everything either. 17 D is a forecaster often on tv...., 'welcoming a' indicates an addition to that.
Gitto, the thematic clues give answers that only differ by one letter from the final entries so they should be easily sorted. 41a is parsed as reversal of the entry with a 't' at the start.
I had a good start with this, getting the theme with only two clues solved. Mind you there had been a programme on the subject on Radio 4 Extra when I went to bed last night, and it was still going through my head!