cheers for the replies gents
the crack is right where the stud is for the other aluminium piece that bolts onto the sump and goes under the downpipe. When i took it off it just fell apart so I guess that took most of the bump and the stress on the stud cracked the sump.
It was a bugger of a job and there was a fair amount of tool improvisation, the rear mount bolt was a big git and slowed progress by about 30mins
if anyone else needs to do this in future....
remove the piece that runs accross sump under downpipe (mine fell to pieces).
undo the exhaust support from the sump and loosen the 19mm bolt.
I found that 5/6mm allens did the trick for cracking the 14 ribe bolts...then a long skinny screwdriver to wind them out. the trickiest being two near the flywheel, and the one near the cv joint.
lastly there is a 13mm bolt running horizontaly through the sump near the cv joint, you need to get to the other side of this as well because there is a nut on the inside end of it.
After all that the sump can be levered away from the block (might take a few whacks with a rubber mallet, once it drops about 1.5"'s you can get access to the oil pump pickup, undo one of the 11mm bolts completely and slacken off the other, whichever one is easiest.
Then a few seconds later of wiggling and the sump becomes free.
all in all about 3.5-4 hours start to fnish and that was after getting stuck a few times. I imagine it'll be a little quicker to put back now I know where everything is, and the best ways to access them.
So sump hunt begins..... public transport until then though