Well folks with some trial and error, and your excellent advice i am getting somewhere...
strip out the drivers side carpet and seats again tonight - hosepipe all over the place with observer in car - 30 minutes and nothing

decided to set garden sprinkler under car - 30 minutes later still nothing
Removed the scuttle trim seal, had a peak underneath and not a lot there - a few dry leaves but not much else, bit more on the passenger side if anything, maybe because the pollen filter housing causing more hidden nooks and crannies.
Pretty much gave up at this stage - decided to put newspaper under the carpets and leave carpet loose so i can inspect regularly for signs of entry point. Then thought i'd give the old shed a wash, lots of water - no wonder not much left in the Welsh reservoirs

- decided to lift carpet on the off chance - wet newspaper on the drivers side corner of the footwell, where the cable loom runs from the fusebox and the bonnet release cable runs. Poured some water directly into the scuttle area, around the point where the bonnet cable comes through - all water ran out into the wing area, clearly visible by removing the side indicator unit.
So it might be the bonnet cable hole or maybe a cable grommet, but i'm getting nearer

So tomorrow night will be removal of scuttle plates (need to get wipers off first), and also remove wheel arch liner for a decent look. Judging by the amount of mud under the arches when i bought this car, i suspect there will be a fair amound at the base of the wing behind the mudflap and arch liner.
Many thanks for your continued effort with the trouble shooting - i think i have light at the end of the tunnel now
