Engineering works on the West Coast Main Line are set to cause severe disruption for rail passengers over the Easter bank holiday weekend.
Shawfield junction, south of Glasgow, is undergoing a £4m signal and track upgrade which will not be completed until Tuesday morning.
Passengers travelling between Scotland and northern England will be affected.
Network Rail admitted the work would cause disruption, but said a short-term line closure was unavoidable.
National Rail said journey times to or from Scotland could be considerably extended over the bank holiday weekend.
There are no train services running north of Lancaster, which means rail replacement coaches will operate between Glasgow and the north of England on Saturday, Sunday and Monday.
In addition, the closure of London Euston station means passengers will have to change services in order to reach the English capital.
Virgin Trains has recommended that passengers avoid travelling.
Donald Morris, Network Rail infrastructure projects programme manager, said: "Our engineers will be working hard to complete this complex programme as quickly as possible for passengers.
"The West Coast Main Line plays a key role in the economic life of the country - carrying passengers and freight - and this work will help improve its reliability.
"We understand the inconvenience this work may cause to some passengers and residents, but such a huge investment in the railway cannot be delivered without a short-term closure of the line."
Further south on the West Coast Main Line, engineers will also be carrying out work between Beattock and Abington in South Lanarkshire.