Wallasea Island is a good start – now for the rest of our coastline | Patrick Barkham

If climate scientists' predictions are right, it will become impossible to maintain our sea defences. This project shows what managed realignment could do

Britain became smaller over the weekend, with the redrawing of our coastline to create Europe's largest man-made nature reserve. Sea banks were breached on Wallasea Island, Essex, as part of an RSPB scheme to restore farmland to its natural state - mud flats, salt marsh and shallow salty lagoons. The coast here is being reconfigured with new sea banks constructed from soil and clay excavated from Crossrail's tunnels beneath London.

The first such "managed realignment" of our shores was in 1991, on the Essex island of Northey, which became famed as a place of retreat exactly 1,000 years earlier when Earl Byrhtnoth ("bright courage" in old English) charitably withdrew to allow 3,000 Vikings on to the mainland to fight his small army. Byrhtnoth's retreat had disastrous consequences but the redrawing of coastal maps for conservation and sea defence is a more uplifting story.