At last I have the answer to a question that has nagged me for 15 years !
When I started having an interest in vintage mountain bikes, I quickly got a soft spot for the very early stuff for reasons too long to explain here (and who cares ?!). And when I finally found the "bike of my dreams" (with lugs !), it was that not once but twice. Firstly because it was a 1985 so just a year after the new trend had arrived here in France and secondly because its make was Bertin, a french brand I favor and collect.
But upon closer inspection, something was off. Only the crankset (Nervar) and rims (Rigida) were french at a time when France still had a strong industry. The rest was from Suntour, Shimano, Tange, L. Sin (?), Brooks and Sturmey Archer. And no catalog, advertisement or press article was to be found anywhere with my bike in it. It was puzzling but then I got to know about british brands here on Retrobike and I thought some bikes from Dawes, Claud Butler, Raleigh, looked very similar. So I started thinking that maybe it was a case of rebadging which could be explained by commercial relations that Bertin had with a british importer/wholesaler named Ron Kitching. But despite the strong feeling, no real match ever appeared. Until now !
That Saracen of yours has all the frame details that puts an end to my investigation : seatstay caps, chainstay dimple, Suntour rear dropouts, lugs, fork crown, cable stops are identical. Drum brakes are a rarity on MTBs and there they are, from the same brand Sturmey Archer. Even the stem, handlebar and headset are identical. Other components differ though like derailers, shifters and brake levers but that's not relevant as the rest is more than proof. Oh and my bike also came with rear rack and mudguards but I removed them thinking they were previous owner's additions but evidently not.