Courage plucked (thanks to all who supplied the moral fibre) front coil removed - not too difficult at all.
Front and rear plug electrode colour looks fine (textbook biscuit colour). Front plug and coil external appearance was quite dirty and it looks like signs of arcing. Suprising what must have got past the seal at the top of the coil. Looks like this may have been causing the misfire.
Two new plugs fitted, coil cleaned up and front and rear coils swapped as suggested to see if fault switches cylinders.
All back together, run up and seems fine - done about 60 miles so far and it's going as well as ever. (which seems pretty good to me!) EcmSpy looking healthy and no fault codes. Fingers crossed!
Should have replied earlier, I'm in Dunmow, Essex.
The advice and offers of help have been much appreciated, hope I can reciprocate at some point.
Thanks.