Commuters travelling from St Albans and Harpenden stations could suffer even crowdier trains next year.

East Midlands Trains is planning to stop calling at Bedford and Luton during peak times from May 2018, and passenger groups predict the reduction in service could cause more crowded Thameslink services.

Chairman of the Association of Public Transport Users, Neil Middleton, said: “While we know the extra fast train per hour for Thameslink will have some impact on East Midlands Trains, we are baffled as to why, even after an increase in the fleet size of three, there is still insufficient capacity to call at Bedford and Luton in peak hours.”

Thameslink services have been undergoing engineering and construction work which was due to deliver benefits from May.

But passenger groups argue customers will now not benefit from the changes until 2020, when the electrified service is extended to Corby.

Chairman of the Bedford Commuters Association, Arthur Taylor, said: “This is very disappointing.

“Local train users have put up with the downsides of the Thameslink Programme construction works - more delayed trains, slower journeys for those travelling to East Croydon and Gatwick, and no services to London Bridge.

“Now we discover that none of us will get the full benefit, probably until December 2020.”

Fast services to and from Bedford are being introduced in May, which will increase the number of services stopping at St Albans according to Thameslink.

Chief executive Charles Horton said: “At the Department for Transport’s request, we have changed our timetable to deliver a continued, fast service into London for Bedford and Luton customers in the peak. There will be six fast trains in each peak at 30-minute intervals which provide better spacing than the fast East Midlands Trains services they replace.

“We will still be giving passengers more peak time seats on the new, cutting-edge, longer trains we are adding to the route. Thanks to the massive £7bn Thameslink Programme, there will be thousands more seats each morning at Bedford and Luton into London and, at many other stations on the north Thameslink route, there will be a significant increase in seats and capacity.”