LONDON UNDERGROUND (LUL) is this week urgently examining 42 sets of points across the tube network after it discovered that they could be a cause of derailments.
The move comes after London Underground revealed that last week's Central Line derailment at White City could have been caused by the same points problems which led to the Camden Town derailment last October.
The same type of points are used in 42 locations across the network.
The Camden Town derailment occurred when train wheels climbed up and then off a newly installed rough section of track (NCE December 4 2003).
The problem was traced to a switchblade rail which has since been redesigned.
But Northern Line contractor Tube Lines admitted on Tuesday that cracks have appeared in the newly designed switchblade rail after just 10 weeks in operation.
Routine weekend inspection revealed 'a small crack' in the new narrower rail last weekend.
The switchblade was closed off on Monday and replaced overnight with a similar shaped rail. The crossover was back in action by Tuesday morning.
'It's all up and running now, but we've got a 10mph speed restriction for the next seven days as a precaution, ' said a Tube Lines spokesman.
He added that there was no danger of another derailment at Camden Town because of a permanent 15mph speed restriction and nightly track inspection.
LUL is leading the investigation into the White City derailment, aided by Central Line contractor Metronet and rail union officials.
Rail consultant AEA Technology is examining the fixed rail and switchblade from the White City points. It looked at track at Camden Town.