Well after the most annoying, solution sorting week, my driveability problems has finally been solved, and because I hate reading forums where there's no outcome to problems posted, here's mine.
After niggling problems , leading to disasterous driving conditions, the one thing that has come out of this is WRITE DOWN WHEN YOU DO MAJOR THINGS that can have an effect on the cars/motor operation.
To cut a long story short, last year I swapped in a new 02 sensor, then some months later did the other one, but I had forgotten that the car had not been driven further than around the block during that time. By the time I got around to driving it properly some 4 months had past so when this problem arose I had forgotten what had changed.
So, the new 'universal sensors' have been sending incorrect info to the ECU which leaned out the fuel/air so the further the car goes, the worse the problem gets. The ECU has a base A/F ratio it can run on if the sensor fails, (hence the ok driving after the ECU is disconnected) but if it gets incorrect info it just follows what its told. Eventually, for me this meant a motor trying to run on a very, very lean air/fuel mixture.
New 02 sensors will be installed in coming weeks, but in the meantime, I have disconnected the 'universal' items to run, pain free, on the ECU's base setting, which is probably how it was before I tried to 'fix' the problem.
Thanks to all that tried to help.