One factor that is forgotten in the debate over the best way to win renewable energy from the Severn Estuary is the threat of sea-level rise as a result of global warming.

This could eventually drown Cardiff, Newport, Gloucester, Weston, Portishead and many smaller settlements.

Important food-producing land would disappear, as indeed would the mudflats that are so important for birds; it would also swamp Hinkley and Oldbury nuclear power stations.

The barrage could prevent this, but has severe impacts. Therefore, the tidal reef is the best option, since it has less environmental impact but comparable electricity output to a full barrage.

The reef could be converted into a wall to hold the sea back if the worst comes to the worst.

Dr Richard Lawson Prospectice Parliamentary Candidate for Weston Green Party North Somerset