Rail staff noticed smoke pouring from a train but decided to continue its journey for a further ten miles until it burst into flames, it has emerged.

Today, officials from Her Majesty's Rail Inspectorate were probing the blaze, which engulfed the 11.24am Skipton to Leeds service yesterday.

Seven people - including a pregnant woman - were taken to hospital for the effects of smoke inhalation, after all 80 passengers were helped from the train by firefighters.

The 35-year-old Class 308 train is among the oldest in Northern Spirit's fleet and is due to be replaced early next year, rail bosses say.

But passengers from the stricken train, which limped from Crossflatts to Armley at reduced speed after the train crew noticed the problem, today questioned why it was not stopped immediately.

Instead, the train continued on the route via Saltaire and Shipley stations, finally stopping at Armley, three-quarters of a mile from Leeds station. It was there that the flames took hold of the middle one of three carriages.

Nigel Patterson, the managing director of Northern Spirit, said: "The fault was identified at Crossflatts and the train progressed towards Leeds, operating at cautionary speed levels. The fault was being continually monitored by the train crew.

"The staff performed within the safety standards that are laid down to the best of our knowledge.

"The train crews are trained to handle these situations. There was liaison that took place, regarding the train continuing to move to Leeds. The investigation is continuing to ensure all procedures were fully followed."

New trains costing £35 million are due to be introduced on the Airedale and Wharfedale routes.

Station officer Steve Wray, of Bramley fire station, said: "The fire was in the wheel bogey - the motor unit underneath the train - it had started in built-up grease and debris and spread to the outside of the train carriage. The middle carriage was heavily smoke-logged."

Once they were switched off, the blaze was quickly tackled. Passengers, including disabled people and babies, were helped off the train with ladders.

Glenn Dickson, a builder from Bradford, was working on the building site next to where the train came to a halt.

He said: "We could see what was happening and were telling the passengers to get off but the train crew was telling them to get back on. I don't think the train crew handled it very well," he said. "They were panicking."

Emma Bird and her friend Catherine Bell, who both boarded the train at Keighley, said they noticed a "horrendous" smell of burning as far back as Saltaire.

At Saltaire, staff had told passengers to evacuate the middle carriage but had then said that there was not a problem.

"But from Shipley you could see blue smoke and we thought there must be a problem, this can't be right," said Ms Bell. "But they let people get on there as well."

Northern Spirit technical director Brett Kibble said staff had not yet discovered the cause of the fire. A full inspection was being carried out at its depot in Neville Hill, Leeds.