Radar guns, such as those used to trap speeding motorists, are to be employed on a stretch of the non-tidal Thames, writes Elaine Fogg.

The National Rivers Authority, which manages the 135 miles of the river to be

covered by the guns, between Cricklade in Gloucester and Teddington Lock, proposes an 8kph speed limit (approximately 5mph). Knots were ruled out as a measure as being unfamiliar to many river users.

Over the next few weeks NRA navigation staff will take the names of speeding boats. Crews will be approached as they slow to navigate river locks.

John Redmond, navigation and recreation manager for the NRA, said yesterday: 'We will use a softly, softly approach to educate and will only resort to court if we get persistent abuse or someone blatantly breaking every rule in the book.'

The radar guns will be attached to fixtures on river banks.