Cyclists are threatening to boycott the London to Brighton bike ride this Sunday because they will not be allowed on trains with their bikes.

Southern and Thameslink say trains cannot carry the thousands of riders travelling to London from Sussex for the start or returning to the capital after the ride.

The new Electrostar trains do not have enough room. Previously, cyclists who had pedalled the 56 miles to Madeira Drive, Brighton, were able to use the old slam-door trains where there was space for cycles in the guard's van.

Southern first announced its ban before last year's ride, causing a storm of protest from cyclists and clubs. This year the ban has been extended to Thameslink trains.

Security guards were on duty at Brighton station last year to prevent cyclist flouting the ban. There were angry scenes as many unaware of the restriction were turned away.

Even before the ban there was congestion at Brighton station with participants trying to find a space on already-crowded trains for themselves and their bikes.

One of those refusing to take part in this year's run is Chris Brady, who lives at Harlington and was planning to ride from the start on Clapham Common.

He said: "I have ridden on at least 15 runs. I will not be participating this year due to the rail companies' utterly disgraceful refusal to carry bikes on the day.

"It makes it impossible for me to return home. It is the Heart Foundation's loss."

Mike Burgess, of the East Sussex Cycling Association, said: "There are a lot of cyclists who are put off from taking part because of the difficulties they have in getting home.

"Some cyclists are not travelling on trains to time trials and races because of the anti-bike attitude of train companies. It makes a mockery of us all being told to use public transport."

Sunday is the 30th anniversary of the ride, which raises funds for the British Heart Foundation.

Up to 27,000 cyclists are scheduled to take part and it is hoped more than £3 million will be raised through sponsorship.

The rail ban means many cyclists have to ride home, stay overnight or arrange transport to take their bikes home.

There is a park and ride scheme at Brighton racecourse for people arranging transport back with their bikes and the British Heart Foundation provides a truck and bus service.

A spokesman for Southern said: "New trains do not have the capacity to meet the needs of the London to Brighton Bike Ride.

"The seats are not removable and there is no separate guard's van as on the slam door trains."