TheFrendo dd has an offer for maths from Durham. (A A A). What they said was that if you did the MAT and gave them permission to access your results then it would speed up the offer.
Dd didn't do too well in the MAT (she reckons 49-52%) as she was ill on the day but decided it was worth giving it to them.
I believe they are standardly very slow (March is not unknown) and are also dreadful about letting people know where they stand on offers day if they haven't made the grades. I think they've been given formal warnings on that, as if they don't either accept or release it means that people can not get accommodation for their insurance or are at the back end of clearing.