This message came from the BBC in response to the the same question sent to them:-
I should state that all the music in the advertisements was listed as incidental and it is therefore not possible for us to provide you with further details at this time. Many programme makers provide details of the theme music in their productions and often some of the other notable pieces or performances which are featured. However, much of the music can be taken from library sources, specially composed for the programme and not commercially available, or simply not listed in the production information we have access to. For these reasons, we are not able to research the origins of music you are interested in.