Many thanks for the replies. After I had commenced the thread, I used my loaf and googled 'Concorde Flight Engineer' and found a shed load of former Concorde flightcrew (including flight engineers) are now plying their trade as guest speakers. For those who are interested, the following link is:
http://www.concorde.demon.co.uk/html/our_speakers.html
From a review of the relevant profiles, as HD suggests, the usual path seems to have been from flight engineer on other aircraft types within BA (B747-136, VC10) and promotion to Concorde. Alternatively, recruitment was from the RAF, then the path above.
One of my original reasons for posting was that I (no doubt in keeping with many others) who wouldn't have necessarily made the grade for pilot would have relished the opportunity to apply for flight engineer at the time. As we know, with the advent of the digital age and demise of analogue flight systems, flight engineers are an endangered species!
My other observation is this. The role of Concorde flight engineer appears to have been a very responsible job. I recall from a BBC documentary, the flight engineer had to move the fuel from various tanks to keep the aircraft in trim but more importantly, this was a time critical activity due to the sheer speed one was travelling and one couldn't afford to be distracted.
On a lighter note, as vctenderness hints at, I imagine being on BA001 repeatedly, the crew breakfast probably become a rather dull affair after a while! Anyway, many thanks for the replies, appreciated.