KEYS TO KNOW

Where is it: Cerboli Island, Tuscany, Italy. What is it: Ten acres in the Tyrrenean Sea, near Elba. Good points: It is perfect for snorkelling and diving and accessible from the mainland. Bad points: While there are ruined buildings, planning permission to develop further has so far proved sticky. If it was approved, the value would increase dramatically. Price: €4 million (approx £3,555,240). Contact: www. privateislandsonline.com.