A further update:
Disconnected every electrical connector/component under the bonnet, sprayed them all with circuit board cleaner, replugged them in, refitted the accelerator assembly.
Started the engine and it would idle beautifully but wouldn't rev over 1,700 rpm.
While it was idling I disconnected the air mass meter, engine died instantly. replugged it back in and now I am back to my original problem again: car sort of starts, feels like it is firing on only a couple of cylinders and is lucky if its at 450 rpm, accelerator has no effect on revs.
Redid all the connectors/components as first time, but no improvement
Some help would be appreciated