well I 'd certainly re-stake it. do you have any pictures to add to show what it looks like at the base. Are there any toadstools around it?

I would re-stake as SBG says. I bet it's the extra height and the sudden extra rain and wind.
Two stakes, one either side, about 2ft apart, away from the rootball. Then fix a crossbar to them, at about a third the height of the tree. Firmly secure the tree trunk/stem to the cross bar, with a rubber cushion between the tree trunk and the crossbar, to prevent rubbing. Hope the process description makes sense. Don't worry about causing further disturbance - better up and straight at this time of year, and it's the best time of year if roots are disturbed.

Yep you both right of course and when tree surgeon spoke to my wife (as I was unavailable) that's what he said straight away. Didn't mention HOW to stake it though so I was thinking of an angled one, into the wind etc. HC, I've seen council tree planters doing the 2 stake thing so I get what you mean. Are we talking round stakes and cross piece? And how would you attach the crossing piece, screw or nail? Am thinking nailing would disturb the posts?
HC, I find it hard to believe it's not a gonner, seeming as it does to have no anchoring roots on one side. Are you telling me it would re-establish given time? And one last question..did I release it from the original stake too soon or actually too late, i.e. not letting it take over and root properly? Thanks both of you for coming back.

many trees partly uproot in the wild and as long as there are enough roots to gain water/nutrients etc it will survive. at my palce of work there is an oak that was partly uprooted in the 1890's and it is still going strong. At the time it was propped with a pit prop apparently to help give it support. a bit like the great oak in Sherwood forest.

Thankyou SBG for that, I'm getting more hopeful about the big stake-out tomorrow (Sunday). Not poss today due commitments elsewhere but first job tomorrow before the storm supposedly hits on Monday.