A major project to upgrade a section of the East Coast Main Line will cost �56m, according to Network Rail.

The rail track company also confirmed a diversion of the line, at Dolphingstone, East Lothian, will be completed by May 2003.

The development covers 1.8 kilometres of track and bypasses old mine workings, some of which date back to the early 18th century.

The track company has reached an agreement with the train operators to ensure that the work is carried out at times that will minimise disruption to passengers.

East coast main line

The line runs for 632km It links Edinburgh and London It carries 1,900 passenger and 250 freight trains per day Current projections are for a 40-50% rise in passenger traffic Train operator GNER is spending �39m to improve diesel and electric services

Network Rail's head of investment Jim Bellington said: "This is one of the largest railway engineering projects of its type in the UK.

"We currently have some 200 engineers staff working on the site.

"Network Rail is committed to providing a safe and reliable rail network.

"Safety has to be our number one priority and we acted immediately after issues were identified at Dolphingstone which could have threatened the integrity of this key cross border route."

'Minimum inconvenience'

Bill Ure, secretary of the Rail Passenger Council in Scotland, said: "We are very pleased with the progress of this multi-million pound project.

"It will ensure that passenger and freight services continue on the east coast main line with the minimum of inconvenience during the engineering work."

Passengers are being advised to contact train operators or contact National Rail Enquiries for information about potential delays.

Engineering checks revealed the extent of the problem

Network Rail said more than 75% of the 1,860 concrete piles required for the operation are in place.

They will support three giant concrete slabs of 340 metres, 328m and 200m in length, which will form the basis of the new railway line.

News of the problem emerged in March this year when a 20mph speed limit was imposed.

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.