Rail firms have ramped up warnings to passengers travelling over the Bank Holiday weekend with major engineering work affecting several lines.
Virgin Trains issued an alert stating that its services will be 'very busy'.
High demand is expected for east coast trains between London King's Cross and Scotland due to passengers seeking alternative routes to and from London because of the closure of London Euston on Saturday and Sunday, as well as Edinburgh's festivals coming to an end.
A Virgin spokesman said: "We expect our services on both routes to be very busy from Friday to Monday, and are advising customers to avoid travelling on our west coast route on Saturday or Sunday unless necessary.
"If customers choose to travel, we strongly recommend they book their tickets in advance, make a seat reservation and allow longer to get to their destination."
London Waterloo services - which have been disrupted for more than a fortnight as part of a major project - have been reduced even further until Tuesday.
Fewer than half of normal weekday services will operate as 14 platforms are closed to enable platforms to be extended to accommodate longer trains, boosting capacity at the UK's busiest station by 30 per cent.
A Network Rail spokeswoman said: "We apologise to our passengers for the added disruption to their journeys and thank them for their patience.
"This all about delivering a bigger better Waterloo station fit for the 21st century."
National Express, the UK's largest coach operator, is putting on an extra 4,000 seats over the weekend to destinations affected by the Euston and Waterloo work.
Travel warnings have also been issued to motorists as traffic is expected to rise by a fifth compared with last year's summer bank holiday.
Some five million motorists are expected to embark on leisure journeys on Monday, up by nearly one million on the 2016 figure.
The RAC recommended drivers wanting to beat the queues this weekend should avoid Friday afternoon and evening, and set off early if travelling on Monday.