I've just followed tjspiel's sensible advice and looked everywhere for date codes. And I found some on both of my wheel hubs. They're both made by Maillard in France and the front hub has [27 84] and the rear hub has [38 84] stamped into them. This means the front hub was made in the 27th week of the year 1984 and the rear was made in the 38th week of 1984. So the bike must have been made in 1984. I'll upload the pictures later. At least I'm getting closer - now all we need to find out is the actual model!

Couldn't find any more serials or numbers on or near the bottom bracket though.