COUNCIL bosses may sue contractors working on a controversial pedestrianisation project, a report has revealed.

The £6.5m Pedestrian Heart in Darlington was delayed when a mechanical digger hit a 100-year-old gas main that was not buried as deeply as plans had indicated.

The discovery meant that the pipe under the town centre - one of the main supplies into the town - had to be re-routed, costing Darlington Borough Council an additional £700,000.

Following the discovery, councillors demanded to know why more had not been done to locate the century-old pipe.

Now, a report to councillors explains what led to the blunder.

It reveals that before work started, Gillespies - the lead consultant on the project - identified trial trenches should be dug to look for pipes.

However, instead of trenches, much smaller scale trial holes were dug - but these failed to identify the shallow gas main.

John Buxton, director of development and environment for the council, explained in the report: "Gillespies identified in early 2005 the need to have trial trenches...a quote was obtained but due to what was considered to be a high cost, it was decided to wait."

Once Birse had been appointed to carry out the work, the holes were dug, but not the trenches.

The report does not apportion blame, but advises councillors: "Members ought to be aware of the current ongoing legal relationships between the council and some of the parties and the possibility that there may be litigation in regard to the subject matter of the review at some point in the future."

Gillespies, as the lead consultant, takes overall responsibility for the scheme.

The report says that the council considered a redesign for the Pedestrian Heart project, rather than diverting the gas pipe.

However, the old pipe would still have needed to be replaced within 25 years.

Mr Buxton said he was very grateful to Balfour Beatty and United Utilities for completing the diversion within three-and-a-half months - when the work would normally take six months.

He said that, even if the shallow pipe had been discovered before work started, it would still have needed to be re-routed.

The council will have now to pay about £200,000 more it would had it known about the pipe before the scheme started.

The Pedestrian Heart has been controversial, as businesses say the ongoing work has reduced trade. The project should now be finished by next June.