Rail bosses admitted today they had no idea when disruption hitting the Norwich to Sheringham line would end.

Passengers on the Bittern Line have been hit with slower running trains and cancellations this month after a near-miss at Thorpe End level crossing.Network Rail said these speed restrictions would stay in place for safety reasons while they investigate how a new Greater Anglia train came within 0.25 seconds of smashing into a car when the crossing's barriers lifted too early on November 24.

A spokesman said they were investigating how train wheels connect with track signalling, as well as the impact of leaves on the line.

However, he could not say how long the investigation would last or when a normal service would run again.

In his weekly message to staff, Greater Anglia's managing director Jamie Burles said the speed restrictions would remain in place until Network Rail changed the signalling system, which is different to other lines in the region.

"Network Rail and Greater Anglia colleagues literally worked through day and night to fully understand the causes," he said.

"Network Rail installed sophisticated signal measuring equipment on Norwich-Cromer-Sheringham line to gain vital information on what was happening, particularly regarding level crossings.

"The information that came back showed the signalling system wasn't picking up both old and new trains as strongly as Network Rail would like."

Mr Burles added that the service was better than last week when 80 services were cancelled every day across the network.

But that disruption has put back the testing of Greater Anglia's new fleet of trains and driver training. He said that would cause some cancellations on routes out of Ipswich.

Mr Burles also took a swipe at the media in his weekly message, accusing it of "incorrect headlines" for stating that the company's new Stadler trains were the cause of problems.

Greater Anglia is buying 58 new Stadler trains and around 20 are now in service.

The trains have had issues with their software and, according to drivers, have had problems connecting to the track.

One also had an issue switching between diesel and electric power.