Just thought I'd update this, the drawer bottoms where fully fitted in at gluing stage, there would be absolutely no chance of clamping them out of square, they are domino'ed at the back and a very deep dovetail at the front. I'll just have to be more careful next time when gluing up the table.
So I tried 2 methods I'd been thinking of, on one I added a wedge to even it up as its rammed home, this worked very well but once in about ten times it sort of catches as I'm closing it, bit of wax will sort it I should hope. The other one was very very nearly in line so I decided to plane it out. Worked well but I wouldn't do it again as it would be all to easy to make the edges of the drawers look wrong.
Thanks for all the advice!