Delays of about 45 minutes were expected on trains on the GNER services from York to London today due to a diversion via Hertford and the Railtrack-imposed speed restrictions.
A GNER spokesman said trains from London were "likely to be full" this afternoon because of the start of the half-term holidays.
Travellers should ring 08457 484950 or 08457 225225 for more information.
Meanwhile, the family of a Yorkshire victim of the Hatfield rail crash have spoken of their loss of a "fantastic husband and father".
Peter Monkhouse, 50, from Headingley, Leeds, who was the managing director of Q Marketing in the city, was killed in the derailment while returning from a London business meeting. In a statement his wife, Susan, 49, and children Nick, 26, Claire, 23, and James, 15, said he was a keen golfer and Manchester United supporter, who enjoyed walking the family dogs, travelling and socialising.
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