East Midlands Trains services 'returning to normal'
East Midlands Trains said services on the Midland Mainline were returning to normal following a signal failure in north-west London.
The problem at Hendon - which has now been repaired - forced the suspension of trains between St Pancras and Luton.
Full signalling has been restored, but passengers were being warned to expect some delays and cancellations on the mainline during Friday evening.
Tickets were being accepted on other routes, according to the firm.
A spokeswoman for East Midlands Trains said: "Services on our network are beginning to return to normal after full signalling was restored in the Hendon area.
"However, there are likely to be knock-on delays throughout the evening peak as a result of the earlier problem. We would like to apologise to passengers for any inconvenience these delays may cause and would like to thank them for their patience."
The company has also said any passengers who were unable to travel on Friday due to the disruption would be able to use their tickets on Saturday.
The Midland Mainline runs between Sheffield and St Pancras, with stops at Chesterfield, Nottingham, Derby, Leicester, Kettering, Bedford and Luton.