Gangs who are illegally digging up bait from a riverbed could cause flood defences to collapse if they are not stopped.

Environment Agency officers have warned homes and farmland could be swamped with water unless the bait diggers, who sell worms to fishermen, are caught.

A gang threatened to punch a senior agency officer who confronted one gang as he took his dog for a walk.

Ray Kemp, a public relations manager for the agency, was out for a stroll along the River Adur at Shoreham on Saturday when he spotted three men on the riverbank with a dog, buckets and forks.

Mr Kemp challenged them and was told they would "stick one on him".

He said he was also threatened by their large vicious dog, which was growling at passers-by.

The agency has faced increasing problems with bait diggers on the river between Shoreham and Bramber, near Steyning, where tidal flood defences are being weakened along the banks as a result.

Mr Kemp said: "I saw them pass the sign that warns the public that digging for bait is prohibited.

"Then I saw them start digging away.

"I had to pass them because I was with my dog. They had a pretty vicious dog with them that was growling.

"I asked them to keep it under control and then I said 'You do realise you shouldn't be digging?'

"One of them threatened to punch me. We have been trained under these circumstances to turn away, which is what I did.

"They must have been digging up worms to sell as bait to fishermen. It's becoming a real problem.

"They used to dig on the beach but, where the sewage treatment seems to be working and the sea is cleaner, there are not so many worms there now so the gangs have moved on to the rivers.

"When I went down the next day there were more people digging away.

"It's an ongoing problem and, if it continues, the flood defences will collapse."

The agency has now stepped up its patrols along the river and has warned members of the public not to approach gangs of diggers.

Some of the highest tides of the year are predicted for the Easter weekend so flood defences along the stretch of river are essential.

Rupert Clubb, Sussex flood defence manager, said: "Bait digging is an offence under the land drainage bylaws.

"The problem is if people dig into the tidal bank it could weaken it and cause the banks to slip.

"If that was to happen the low-lying land behind could be at risk of flooding.

"You have to catch diggers in the act in order to prosecute them but we have managed to enforce boats speeding on the river so I'm sure we can tackle this in a similar way."