In reply to stroppygob:
> This is weird, was it not published as part of "Secret Pilgrim"?
Looks like it - I know nothing of these matters, but three minutes of zinging around Amazon UK and US, and Abebooks, and Wikipedia, suggests that A Spy in His Prime is the title only of an audiobook version of the third chapter/story of The Secret Pilgrim...though I'd have thought that an actual fan, such as the OP, would know this already...?
http://en.wikipedia.org/wiki/The_Secret_Pilgrim#Part_three