Rail services south of Edinburgh are being held up amid fears of subsidence beneath the tracks caused by disused mine workings.

Railtrack is carrying out drilling operations on a stretch of line between Prestonpans and Wallyford, in East Lothian to determine the extent of the problem.

A 20mph speed limit has been imposed.

Similar problems on a nearby section of track cost more than �6m to correct and involved a temporary re-routing of the line.

Last year, the UK Government announced it would not be awarding a 20-year franchise to either of the two train companies bidding to run the East Coast line.

Inquiry findings

The second stage of the line's upgrade will not be completed until 2006 at the earliest.

Mines once played a large part in the economy of East Lothian.

In Edinburgh itself, an inquiry last year into land subsidence last year concluded that collapses in 200-year-old mine workings were to blame.

The problem, which first appeared in the capital's Ferniehill area last autumn, spread to Moredun Park and homes in the Gilmerton area.

In 2001, objectors said that a major new dual carriageway planned for green belt area south of Edinburgh could be dangerous because it crosses old mine workings.