An estimated 30,000 passengers were hit when signalling problems caused by a power failure brought services into London's Euston station to a halt.
Virgin Trains, which operates on the West Coast Main Line, came to a standstill after a power failure between Milton Keynes and Bletchley.
Up to 600 were stranded on eight trains and replacement buses covered the 50 miles between Euston and Bletchley.
Virgin Trains said they were running a reduced service for Tuesday evening.
A Network Rail spokesperson said the signal problem had been temporarily resolved and train operators were running revised timetables. Passengers have been advised to check before they travel.
Engineers will be working through the night to restore a full service by Wednesday morning, she added.
Virgin Trains said they were running eight trains an hour on the route.
Earlier, Virgin Trains had to cancel all services in and out of Euston as engineers investigated the problem which struck the service at 0930 BST.
London Midland was also operating a reduced service between Euston and Northampton and Bletchley for the rest of Tuesday.
London Overground services were not affected and were running normally between Euston and Watford Junction in Hertfordshire.
To compound problems in London, a lineside equipment problem at Liverpool Street station led to several cancellations on National Express services to Cheshunt, Enfield Town, Chingford and Cambridge.
There is also a reduced half-hourly service to Stansted Airport.
The London-Scotland route also experienced delays of up to two hours.
Services on South West Trains were also hit during the morning rush-hour following a points failure at Wimbledon, south-west London.
There had been no Virgin Trains' services in and out of Euston over the bank holiday weekend due to engineering work on the London to Scotland West.
The company runs services from London to destinations such as Liverpool, Manchester and Glasgow.
^ Back to top | BBC Sport Home | BBC Homepage | Contact us | Help | ©
~RS~q~RS~~RS~z~RS~43~RS~)