Two stretches of railway track in Oxfordshire have "similar characteristics" to those suspected of causing the Hatfield disaster, it emerged today.

Railtrack bosses named 81 spots on Britain's railways - including the fast track at Didcot East and at Heyford - where there were areas for concern.

But Rail chiefs today told Oxfordshire commuters not to worry, saying any faults would be quickly fixed. Precautionary speed limits of 20mph are now in force on the Didcot East line - the loop skirting Didcot station on the main route to Paddington from Oxford - and at Heyford on the Oxford-Banbury line.

They are said to share the same risk factors as Hatfield. The age and condition of the track is the main concern.

The Didcot East line is also used by high-speed trains and on a bend, which adds pressure to the line.

Thames Trains said today it did not expect delays. Spokesman Martin Walter said: "Safety is always going to be the main consideration. We have to be careful not to blow this up out of all proportion. No-one is in danger on that line. "It's the same as a car having a worn out tyre - you'd get it fixed at the next service and that is what will be done."

The news came as a second derailment on a Virgin Cross Country train from Birmingham New Street to Manchester Piccadilly took place yesterday, although nobody was hurt.

Railtrack chief executive Gerald Corbett, whose resignation was refused after the deaths of four passengers in the Hatfield accident this week, said: "The system has been under-invested in for years.

"Safety and investment are the priority."

The number of maintenance staff working on Britain's railways has been cut by 6,000 since Railtrack took control of the network. There were 15,500 maintenance workers in 1998 compared with 21,500 in 1994 when Railtrack took control, according to the National Union for Rail, Maritime and Transport.