Rail passengers trying to use the upgraded £7bn Thameslink service on Sunday were met with mass train cancellations and no information about why services were not running.

A huge publicity drive backed Sunday’s biggest ever timetable change but, despite the big build-up, passengers trying to get into and around London found few of the promised new services were actually running. For more than a year, Govia Trains has been working on an ambitious plan to merge its Thameslink, Southern and Great Northern train operations and introduce a raft of promised improvements.

South-east London was particularly badly hit in the morning, with passengers facing mass cancellations and long waits. Throughout the day, between half and a third of timetabled trains across the new enlarged network were being cancelled.

While the train company had warned the changes would result in disruption, passengers were taken aback at the level of cancellations and were furious at the lack of information.

“It takes a very special rail company to screw up its new timetable as soon as it starts. Trains cancelled and a reduced service already announced for tomorrow. Well done the @TLRailUK buffoons,” was one sentiment on Twitter. Others described it as a “farce”. Sunday’s disruption does not bode well for Monday, when commuters would really put the new system to the test, commenters warned.

The biggest change to the London commuting network ever seen allows trains to run from Cambridge and Peterborough through London to Gatwick airport and on to Brighton for the first time, along with a number of other services. The new Govia operation accounts for around a quarter of all UK rail services.

Charles Horton, Govia Trains’ chief executive, said last week: “The 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.” He said passengers would see huge benefits from changes that provide for an extra 50,000 passengers in the capital’s morning peak, with Govia running 400 more trains a day.

However, the new timetable has been criticised for adding to journey times for many. In some towns, rail users’ groups have described the new schedules as a disaster, as their service has been hugely downgraded, particularly off-peak.

The company said: “We apologise to customers for any inconvenience caused during the initial stages of the timetable change.”