There are some key questions to resolve before you take on this plot. The first is whether the foundations were built strictly in accordane with the original planning consent, and whether any conditions attached were properly approved before the foundation works started. If these provisos are met, then the original planning permission remains alive and the scheme could technically be completed.
Importantly, though, you also need to account for structural considerations. Find out exactly what foundations have been built – try contact the original builders, architect or even the local building inspector, each of whom may have a record of what’s been laid. If that draws a blank, you’ll need to have trial holes dug to determine the depth of the foundations and whether they are indeed suitable for continuing the project.
Whatever you do, make sure you take professional advice from an architect, building surveyor or engineer before you proceed. Unless there is certainty over the adequacy of the foundations, don’t be tempted to re-use them.