The tunnel carries thousands of cars every day

Traffic bosses at the tunnel believe 200 "hardcore" motorists using the tunnel each month are causing delays during morning rush hour.

One regular user was sent a written warning after he was caught 14 times failing to comply with lane markings.

Bosses said they are able to take the action because the stretch of road is privately-owned.

Tunnel manager Peter Hedley said the driver was one of three who had been identified and had letters sent to them.

This is the last chance to change their behaviour Peter Hedley, tunnel manager

He said problems were caused at the south side of the crossing by drivers who refused to go in the right-hand lane at a roundabout and instead went all the way around it, blocking traffic coming out of the tunnel.

Mr Hedley stressed that people unfamiliar with the tunnel and the lane markings would not be targeted, but regular users would.

"It is this small percent of drivers that are adding up to half an hour to delays on peak times," he said.

"We can't allow 200 people - that's 0.02% of those using the tunnel - to cause these delays. They will be excluded from using the tunnel if they continue.

"Our monitoring of vehicles has shown there are three regular lane abusers who refuse to heed the warnings. This is the last chance to change their behaviour."

Mr Hedley said when the problem was first spotted and initial warnings issued plenty of motorists agreed to obey the rules.

He added: "Many people stopped doing it and the traffic was flowing better but now we are down to the hardcore."