Govia Thameslink Railway (GTR) has announced there will be a 13 per cent increase in train services in UK's biggest-ever timetable change.

This is part of the rail operator's RailPlan 20/20 programme with almost 400 more trains running every day when its new timetable is introduced next week.

It will start to run around 3,600 trains – one every 24 seconds – across its network in a step forward for its programme to boost capacity across the region.

Passengers are today urged to check before they travel ahead the shake-up, with the time of every train changing on Sunday 20 May.

Departures and arrivals will be re-set across the entire GTR network of Southern Railway, Gatwick Express, Thameslink and Great Northern, which together account for almost a quarter of all UK rail journeys.

Many passengers can expect their trains to start and terminate at different stations, for example many King’s Cross services will instead call at the adjacent St Pancras International.

Passengers will see huge benefits as a result of the changes with space into London for an extra 50,000 passengers in the morning peak.

Due to the expansion, 80 more stations will have direct services to central London stations such as Farringdon, City Thameslink and Blackfriars by next year.

Rail passengers will benefit from enhanced frequency, reliability and connectivity across the network, with significant uplift at key commuter stations such as Brighton, Bedford, Luton and East Croydon.

Some disruption to services is expected during a major re-deployment of trains and crews over the coming weeks.

Charles Horton, GTR chief executive, said: “We are introducing the biggest ever change to a rail timetables to significantly boost capacity on the UK’s most congested network.

"We don’t want passengers to get caught out and so we strongly advise them to look up the times of their trains as they will find that from 20 May each and every one of them has changed.

“Due to the sheer scale of the changes, we will have to redeploy a large number of trains and crews and services may not run at normal times during the introductory phase, although the impact on peak time services during the transition will be minimal.”

“Introduction of the new timetables is a major milestone in the delivery of RailPlan 20/20, our programme to modernise rail services, taking advantage of the new infrastructure and trains provided by the Government’s £7bn Thameslink Programme.”

As part of the decade-long upgrade project, London Bridge has undergone a £1bn rebuild and, in Britain’s biggest fleet order, some 115 new self-drive Siemens trains are being introduced.

Passengers have been asked for their input to the new timetable with 28,000 responses received over 18 months in the biggest consultation of its kind.