THE contractors building a half-mile viaduct for the M74 extension into Glasgow have been banned from re-starting work amid safety fears.

THE contractors building a half-mile viaduct for the M74 extension into Glasgow have been banned from re-starting work amid safety fears.

But transport bosses have insisted the project is still on schedule.

The city's Subway operator, Strathclyde Partnership for Transport (SPT), is refusing to allow engineering work to continue on a section of the Eglinton Viaduct until assurances are given it will not damage the underground train network.

Work ground to a halt a week ago on part of the £692million road project after a crack was found on the wall of a Subway tunnel on the city's South Side, 25 yards from the site where excavations were being dug for the motorway, which will link to the Kingston Bridge.

The crack is said to have caused plaster to fall from the roof of a tunnel between West Street and Bridge Street and led to the temporary suspension of services on the 112-year-old system last Thursday.

SPT said it was waiting for "detailed proposals" from Interlink M74 Joint Venture, the consortium building the new road, over measures that would be put in place to ensure no further damage was caused.

An investigation is still under way by SPT engineers to establish the cause of the damage.

An SPT spokeswoman said: "We have a duty to ensure the Subway operates in a fashion that guarantees passenger safety. We would not be running services if there was any risk to passengers."

"We are in discussions about bringing in a more sophisticated monitoring system in our tunnels so problems can be identified at an earlier stage.

"Our engineering consultants are continuing to investigate the cause of the damage in the tunnel and what measures need to be taken to ensure similar problems do not happen again."

However, Transport Scotland said the project was still on target to be completed by 2011.

A spokeswoman said: "Delays such as this are factored into the overall timescale. This is only a small section of the project.

"This is a matter for SPT and Interlink JV, but we understand they are working together so piling can begin again as soon as possible."

Interlink refused to comment on the discussions with SPT except to confirm that piling work, the process of driving foundations deep underground to support the motorway, would remain suspended until the investigators had found the cause of the damage.

A spokeswoman for the consortium said: "Recommencing the work will depend on the outcome of the SPT investigation.

"We cannot comment on liability, that is a matter for them."

The spokeswoman also refused to speculate on how long the work would be delayed or whether this would force up costs.