A fourth lane of the M6 in the West Midlands, which aims to cut congestion, has been shut to traffic on more than 50 occasions since it was launched earlier this year, it emerged today.

Cable thefts, camera and signal faults have forced the hard shoulder to shut several times between junction 10a at Essington and 8 at West Bromwich since the spring.

The main problems were between junctions 10a and 10 at Walsall which had been targeted by metal thieves.

There were also problems due to a gantry sign having to be removed and replaced.

The extra lane to keep traffic flowing at busy periods was launched by the Highways Agency in March as part of a £150 million scheme.

But information released under the Freedom of Information Act shows there were at least 57 times when it was unable to open. This ranged from hours to days.

It included 20 days for a gantry sign to be replaced southbound from junctions 10 to 10a between March and April, delaying the full launch of the scheme.

There was a 10-day period in September after metal thieves stole cables, knocking out CCTV cameras and signs. Camera faults taking up to three days to repair have also been reported along with signal problems taking up to four days to put right.

Highways Agency spokeswoman Jane Manning said: “Safety is our top priority and the hard shoulder cannot be opened when it is not safe to do so.” The Highways Agency said the costs of repairs are not broken down individually and are carried out as part of a contract.