Passengers will have 32 per cent more carriages and 4,200 more seats on St Albans services from this weekend, according to train operator Thameslink.

Commuters will also be able to travel straight to London Bridge from Sunday after Network Rail completed rebuilding work as part of the latest stage of RailPlan 20/20.

Govia Thameslink Railway (GTR) chief executive Charles Horton said: “We are introducing the biggest-ever change to our 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 May 20 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 RailPlan20/20, our programme to modernise rail services, taking advantage of the new infrastructure and trains provided by the government’s £7bn Thameslink Programme.”

RailPlan20/20 is a series of changes to the Thameslink network designed for stations to accommodate longer and more frequent trains, which included extending the platforms at Farringdon and London Blackfriars.

Train user group London TravelWatch has claimed some credit for several of the improvements, such as ensuring the route through the main St Pancras concourse to the new Thameslink platforms is available to passengers 24/7, so passengers do not have to use Midland Road early in the morning.

The group’s chair Arthur Leathley said: “Throughout the project we have stood up for passengers, particularly when engineering works adversely affected train service performance, and we will continue to monitor this as the new services come in.”

Thameslink is attempting improvements across their line and an upgrade was planned for Harpenden before East Midlands Trains torpedoed it by stopping their peak-time services from calling at Bedford and Luton.

Network Rail asked Thameslink to make up for the lost services at Bedford and Luton and as a result Harpenden commuters will be losing as many as 52 carriages during morning and evening rush hours, according to campaign group Harpenden Thameslink Commuters.

Their leader Emily Ketchin said: “From Monday Thameslink is slashing key Harpenden services by a third. The new timetable sees longer journey times and fewer trains at the times people most need to travel. This will make it harder to get to work, to manage childcare and to even get on a train.

“Harpenden commuters need to let the Transport Secretary know about the impact the new timetable has on their lives and livelihoods.

“Thameslink also has to face up to the realities of commuting rather than hiding behind spin and obfuscation.”

Thameslink has argued that capacity on services to Harpenden at what they consider morning and evening rush hours is increasing, not decreasing.

GTR head of strategic planning Phil Hutchinson said: “For instance, there are currently 10 trains from Harpenden arriving at St Pancras between 0800 and 0900.

“From May until December, there will be nine trains in this period, but with a total of four more carriages.”

For more about RailPlan20/20 visit www.railplan2020.com