The BBC's Alan Whitehouse: "Miles of cabling are slowly rotting away"

The BBC has learned that at least one problem is similar to that which led to the rail disaster at Clapham, south London, 10 years ago.

Railtrack, which operates the UK's track and signalling, has conceded that the fault affects 102 signal boxes all over the rail network.

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The scale of the problem has been highlighted by confidential documents obtained by the BBC.

They show that in some signal boxes the wiring used to link complex electrical switch gear is extremely fragile.

Maintenance workers have been banned even from touching it, in case they trigger a major failure.

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Railtrack officials insist that passengers are not at risk, and that signal equipment is safe unless wiring is disturbed.

In one incident, linked to the state of the wiring, the signalling malfunctioned in almost the same way as the Clapham disaster 10 years ago.