the beema is aliiiive!!!
Turns out that it was simply the return fuel pipe had come off at the engine bay end, quite how i do not know, but the mechanic said there is no evidence of the pipes being caught anywhere along the underside of the car and being pulled off in that way, which is what i was expecting, but all mended now anyway.
Well, until i managed to unplug the passenger occupancy sensor wiring by accident when rooting about under the seat for something earlier on, something i didnt realise i had done until i got back to my place, so as expected, even after plugging it all back in i have an airbag warning light on, ffs lol