‘You have been sat’ would now be considered non-standard, Standard English calling for ‘You have been sitting’. So it is that in the following two pairs, the (a) sentences are also thought to be non-standard:
1 (a) He was stood on the corner. 1 (b) He was standing on the corner.
2 (a) He was sat on a park bench. 2 (b) He was sitting on a park bench.
However, in the next two pairs both (a) and (b) are standard, but with different meanings:
3 (a) He was parked on double yellow lines. 3 (b) He was parking on double yellow lines.
4 (a) He was stopped at the traffic lights. 4 (b) He was stopping at the traffic lights.
3 (a) and 4 (a) describe stasis, while 3 (b) and 4 (b) describe motion. Could not the same distinction be applied to 1 and 2, the past participle suggesting a degree of passivity without the use of the passive voice? Wouldn’t the force of Oliver Cromwell’s speech have been less had he said ‘You have been sitting too long here’?
Caxton 