Improvement work to the East Coast Main Line means there are no trains to London from Cambridge and Peterborough all weekend.
It is hoped the £1.2 billion pound upgrade will create capacity for an extra 10,000 seats and more services into the capital.
Network Rail said the inconvenience to travellers could not be avoided.
British Transport Police officers were stationed at Peterborough to help minimise disruption and help confused travellers.
The work has seen the closure of London King’s Cross for the entire weekend.