Ok so 4th was no go.
Well today the box decided that 3rd was the only gear I was allowed.
I've just driven from Honiton to Gloucester in 3rd only.
Only hassle was the hill start at the beginning (think revs, think clutch smoke).
I managed to get through Taunton town centre OK. Lucky it's 3rd really, because idle is 12mph in 3rd plus max speed is 100odd, so doing 75 down the motorway was easy.
Good job I've got the new box coming then.