We're already on to episode 3 but it is being read by the author (Mark) himself, with typical aplomb.

It was broadcast on Sunday but you can listen to it any time for a week afterwards. As far as I can tell, Radio4 extra is available free online anywhere outside UK.

It's about a British spy, Lucifer Box, and is set between the Wars. Since he is Mark's creation, Lucifer is a flamboyant, resourceful character, a kind of all-action (oh yes) version of Mycroft but with a very different sibling. And possibly flashier clothes.

Mark has also recorded Black Butterfly. Most of what is on this radio channel is broadcast at least once a year, though exactly when varies. 

And please can anyone tell me what the music is?

Just cllick on Radio on the BBC home site, and then Radio4 extra. It broadcasts drama, comedy (including Cabin Pressure) including , book readings etc, no news or music. Most of it was made for Radio4 originally, including all the Merrison/Williams or Sachs Holmes adaptations, and many other good things. They have a special section every day called 'The seventh dimension'  for science fiction, which includes anything from Poe to Red Dwarf. The Lovecraft readings are particularly fine IMO.
It has kept me sane since I left the UK.