I'm sure I will get plenty of replies to this one...

Can someone please tell me the title/artist of the 'trumpet' piece of music in the m&s adverts... Thanks

YouTube - Groove Armada - At The River

Or

YouTube - Santana. Samba Pa Ti

Or

YouTube - Small Faces, Itchycoo Park

according to which commercial you are talking about. The first one has the most trumpet in it.
This may not be the artist that actually did it on the advertisement.