Rail bosses pledged a new timetable would mean fewer delays and more reliable services.

But passengers have faced weeks of disruption between King's Lynn and London.

Services have been delayed or even cancelled, while journey times have also increased.

The Fen Line Users Association (FLUA) says rail companies and politicians had had a long time to prepare for the new timetables.

'Basically, the whole thing is a total shambles,' said FLUA chairman Colin Sampson.

'There have been thousands of cancellations, and although Lynn hasn't been quite as badly affected we are the best of a bad bunch - Ely, Cambridge and stops to London have a huge problem.

'The Secretary of State of Transport, the Department for Transport, Network Rail and rail companies have a lot to answer for.'

Mr Sampson said rail companies have been forced into adopting the new timetable to allow more trains into London and south of the country.

He said a shortage of train drivers trained for the new timetable and additional stops after Cambridge, adding 10 minutes to the journey time, have contributed towards commuter chaos.

He said trains had to arrive within 30 seconds at the right station platform, but one second over would disrupt the entire network.

Sufficient drivers and longer trains could alleviate problems with overcrowding, he said.

A spokesman for Govia Thameslink Railway, which operates Great Northern Trains, said: 'We are very sorry for the continued disruption. This followed the delayed approval of the new timetable, which meant we had to substantially adjust our plans and resources in an unexpectedly short time-frame.

'We are re-planning how we use trains and train crew on Thameslink and Great Northern to deliver a new fixed, interim timetable in July that will prioritise peak trains and reduce service gaps, progressively delivering improvement.'

On Friday Charles Horton resigned as chief executive of Govia Thameslink Railway.

'I recognise that passengers have been hugely frustrated at the significant disruption caused by the introduction of new timetables. It is the right time to hand leadership of GTR to a new pair of hands,' he said.