Trevor
You say you have a signed contract and i assume you have exchaned contracts i e you have a part signed by the Seller
The contract is binding and you should not vacte
You have a real problem on you hands
Steps to taken
1Do not vacate
2 Register your interest at the Land Registry to prevent your sites being sold to a Third Party
3A court case would be expensive and should be avoided if at all possible
4 Seek the advice of a Local Surveyor on plans and site measurements
5I f a new deal is arrived at do not forget to make it a condition that the seller pays all ofyour legalfees and dsbursements including those incurred on your original purchase
Best of Luck