Sorry what is an AST?
The whole patio needs lifting approx 12 slabs, then they need to dig down to investigate why the patio has sunk in two directions and the drain lifted, possibly due to a 30ft silver birch tree in the neighbours garden, then re-sit the drain and lift the step back up into original position. I don't know what hey have been quoted money wise though, sorry.
Apologies again I have just realised
AST = Assured Shorthold Tenancy...
Yes we took the tenancy in July 2008 so I guess it's now a SPT (?)