The operatives, employed by a consortium of Balfour Beatty and Seaboard contracting, also halted their work after the incident.
A company insider said that although the train was going slowly the workers were in danger and there were fears that the safety systems that Balfour Beatty had in place were inadequate.
The insider said: "Had the train been going a lot faster there could have been a serious accident; the workers could have been killed."
He said it soon became clear that the paperwork covering the management of operational movements was not up to scratch.
The review has now been completed and certain procedures and regulations have been revised
Network Rail spokesperson
A spokesperson for Network Rail confirmed that an incident had taken place on 9 May. He said that the gang had been between two "possessions" – sections of track that are not used by passenger trains – when it took place.
The spokesperson said: "The engineering train came through the section of track very slowly at about 5 mph, saw the men in the distance and then came to a halt."
The spokesperson said that Network Rail had carried out a review of all the rules governing this kind of occurrence.
He said: "The review has now been completed and certain procedures and regulations have been revised."
A spokesperson for Sebco, the Balfour Beatty and Seaboard contracting railway joint venture, confirmed that an incident had taken place and said that it had worked with Network Rail on the review.