A GTR spokesperson said: “We are implementing over the coming weeks the biggest timetable change in a generation to boost capacity and improve reliability, introducing 400 extra daily trains and space for 50,000 extra passengers in the peak.“Due to the scale and complexity of the task, these changes will be made incrementally. This involves redeploying drivers and trains and changing operating practices to achieve a large increase in the number of services, carriages and station stops. “Despite some cancellations, passengers will benefit from an overall increase in capacity with immediate effect. The new Thameslink timetable: giving us twice as many cancelled trains to choose from @TLRailUK @acinderellaline #timetable #trains pic.twitter.com/3cY1vumlvv— Dan Robinson (@giantlobsterprd) May 21, 2018 [email protected] 0643 from Flitwick to St Pancras, driver has just said this train is being cancelled at St Albans?! Many others also cancelled this morning. V poor service. #badservice #railplan2020— Jamie Johnson (@jay135769) May 21, 2018 Well played @TLRailUK new timetable,trains cancelled,no drivers……absolute shambles pic.twitter.com/g4Zl2aLiDw— dan johnson (@danlikestea) May 21, 2018 GTR warned that services could be disrupted as the new timetable was introduced, leaving some passengers frustrated on the first day. “We apologise to customers for any inconvenience caused. Anyone delayed by 15 minutes or more can claim compensation through our websites.” “It is our members dealing with the anger at the sharp end not the well-paid top brass from Arriva and Govia who are responsible for this Meltdown Monday on our railways.”Both of these companies have sought to compromise safety and access by hacking back on critical staff and it is no surprise to RMT that they can’t be trusted with the massive logistical challenges of bringing in new timetables.”Frankly I wouldn’t trust the private train operators to run a bath let alone our vital rail routes. After Virgin/Stagecoach were kicked off the East Coast last week it’s time for the rest of these racketeers to be sent packing as well and for our railways to be run by the public sector as a public service.” More than four million trains across Britain were rescheduled from Sunday in the largest timetable change in living memory.The number of alterations is seven times larger than normal due to the introduction of new trains and services following billions of pounds of investment. One commuter complained: “New timetable and a packed train just cancelled as no driver in London to takeover. Triumph of Thameslink.”Another said: “First day of ‘faster and more reliable trains as part of the new timetable’. My train is cancelled, good start @TLRailUK.” Day 1 of the new timetable st Harpenden station – trains cancelled 7:30 & the platform is packed 7:34 expected then not another train till 7:50. 1 train in 25 mins #Thameslink pic.twitter.com/qRUCEzaiZt— Chris Hall (@cjh15) May 21, 2018 @TLRailUK Are you serious? 7.31 cancelled, new 7.54 completely disappeared and the 08.01 cancelled as well just to finish it off. How exactly are you planning to get 3 trains worth of people on the 7.46? pic.twitter.com/I1U71gptXA— Aimee Denholm (@DenholmAimee) May 21, 2018 When one Twitter user asked what this meant, the Thameslink account replied: “With the new timetable being introduced we have a lot of staff and stock in the wrong places. Some services have been altered/cancelled as a result whilst Control work to get everything in the right place.”Great Northern told one customer trains could be altered “for the next few weeks whilst getting everything into place”. The shake-up is designed to increase overall frequencies and reliability, but some passengers will find their regular journeys are no longer possible.The new GTR timetable was developed from scratch and was designed to tackle existing issues by extending stop times at busier stations and increasing turnaround times at destination stations.Many of the timetable changes are a result of the £7 billion invested in the Thameslink programme in the South East, including rebuilding London Bridge station, new trains and track improvements.There will be almost 400 additional GTR trains every day.Some passengers in a number of locations complained they will be served with fewer or slower services, including in Hertfordshire, Bedfordshire, Kent, East Sussex and Surrey, where many people pay several thousand pounds for annual season tickets to London.RMT General Secretary Mick Cash said; “The union is picking up reports from both Northern and GTR of a hopeless lack of planning, combined with a shortage of crew and fleet, which has reduced the Monday morning journey to a nightmare for many passengers. Good start to the new timetable with @GNRailUK train to work cancelled and train home this evening already cancelled too!— Sophie Edwards (@sophiehannah15) May 21, 2018 Angry commuters waited for over an hour on crowded train platforms as scores of trains were cancelled on Monday morning, the first working day of the new timetable across four major operators.Every train run by the UK’s busiest franchise, Govia Thameslink Railway (GTR) – which consists of Southern, Thameslink, Great Northern and Gatwick Express – was rescheduled from Sunday.Officials at GTR were unable to give The Telegraph the number of trains cancelled on Monday morning, but most stations in and around London this morning listed many cancelled services from those operators. Those who managed to cram on to a crowded train faced having their services cancelled while they were on board as drivers were not available in London.Others had their services diverted, with at least one train to Gatwick terminating at St Pancras International. As several people aired their frustration on social media, the train operators said the disruption was due to a “short-term planning amendment”. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.