Tree leaning/falling over

Hi everyone
In the last gales before Easter my plum tree started falling over - it was leaning at about 60 - 70 degrees to the ground and had come away from and broken the trellis it was originally attached to. We propped it up with an old cut-down fence post and all seemed well until today, now the prop has come away, and the tree is now leaning at about 45 degrees to the ground. The tree is about 6 metres tall and the trunk is about 6" in diameter at its widest part. I don't really know how old it is but it was a good size when we moved here 5 years ago.
The roots are making the ground bulge where they have been dislodged but are not visibly protruding out of the ground.
Any suggestions? Can it be saved? Should I consult a tree surgeon and if so, how much is it likely to set me back?

I saw a tree in a garden while I was out walking the other day and they had used the straps that come for strapping down trampolines.  They ran them from the branches to the ground.  They also had three posts around the trunk, driven into the ground and the trunk tied into each of these. 

My neighbours managed to prop up a partially uprooted apple tree (about 8-10 feet tall) for a couple of years, and it fruited well - I think the problem is that once uprooted it's never going to be 100% stable again, especially if you can't get it back completely vertical (sadly, if it's still leaning, the better it recovers, the worse the problem as it becomes even more top heavy with fruit. )

Although they eventually replaced it after it fell over yet again, they may well have done better with the sort of heavy duty supports you are suggesting Stangerachael.

i have no experience of this but if you could get a year or two out of it being propped up could you not look into buying some root stocks and try grafting some branches onto them.

this way you get fruit for another couple of years and hopefully by time it dies you will have one or more new tree's that are is a couple of years old and well developed.