The company has run new ‘preview’ services ahead of opening new routes between Luton and Kent and others between Bedford and Littlehampton via Gatwick and East Grinstead.
These trains, which run through new tunnels brought into use by Network Rail at St Pancras International, will eventually connect passengers directly from 80 more stations in southern England through central London stations such as Farringdon, City Thameslink and Blackfriars.
The new routes, which will be running in May, will create space for 40,000 more passengers during peak periods into London.
GTR chief operating officer Nick Brown said: “This is a landmark moment and shows that GTR is delivering on its promise to give passengers a new, high-intensity service to a greatly expanded network of stations.”
The improvements will increase capacity further to 60,000 next year, he added.
Network Rail’s Thameslink programme director Simon Blanchflower said: “Opening the tunnels for passenger trains between the East Coast Mainline and Thameslink at St Pancras International is a great achievement. It marks the final major infrastructure piece in the jigsaw that opens up the full future Thameslink network and its north south travel opportunities across London.”
Thameslink trains will run from 80 more stations (140 in total) so passengers will no longer have to change if they are travelling to St Pancras International, Farringdon, City Thameslink and Blackfriars in central London. The majority of this improved service starts this May
The expanded Thameslink network means fewer passengers will need to switch to the Tube to complete their journey, saving time on their daily commute
Rail Minister Jo Johnson said: “Passengers on the expanded Thameslink route are now starting to see the benefits of almost ten years of hard work.
“The ambitious £7 billion Thameslink programme – sponsored by this government – is delivering extensive infrastructure enhancements, new trains and a new timetable to tackle one of the busiest and most congested parts of the rail network.
"From May this will result in thousands more passengers experiencing faster, more frequent and more reliable journeys across London and the South East.”