Was surfing some French forums earlier today, and thought about this thread and punched in MBK Pro Racer in the search.
From what I gathered, at least in the the mid-80s there were 3 top flight bike models - no compromise stuff - offered by MBK. This is where it get's beautiful, these were models that were built special order at the same place as the pro team bikes, and also in the offering was custom sizing and obviously all the available trimmings as options. Your frame is one of those. It's a bit like the Raleigh SBDU thing going on.
In '88 the MBK Fagor team also had big rider names, plus a bunch of Irish and Briits in the line-up. That may go some way in explaining how a French high end bike made it's way to the UK. I don't think your bike is pro team bike, but could have been for early season stuff. I think it's more likely whoever bought it initially in whatever country was a serious rider and shelled out a lot of hard cash BITD for something with a similar pedigree to what the pros had.
Someone keeps mentioning the number braze-on. For sure that was specified as an option when ordering. I have seen a similar MBK Pro Racer II on the French equivalent of gumtree, but the frame is different (with a pump peg, long Campag horizontal drop-outs) despite the same paint work and similar decals.
As for the BB being French, I'm prepared to wager it is with a virtual Lidl Pilsner on "that" thread
Eitherway, you have a top notch retro race grade frame, and I'm sure it will ride great.