Hundreds of delegates struggled to get home from Labour’s annual conference in Liverpool after train services to London were suspended.
The West Coast Main Line was hit by a signalling fault as leader Jeremy Corbyn was making his keynote speech on the final day of the event.
No trains were able to operate between London Euston and Watford Junction, which is on the route taken by services to the capital from Liverpool.
This left passengers scrambling to find alternative routes, adding several hours to what is normally a direct journey of two hours and 15 minutes.
Trains serving other destinations such as Birmingham, Manchester, Glasgow and Edinburgh were also affected.
Some lines were later able to re-open, but delays and cancellations were expected to continue until 6pm.
Labour leader Jeremy Corbyn tweeted: “Couldn’t make this up. We need public ownership of our railways.”
Railway signalling is part of the infrastructure managed by Government-owned Network Rail.
The fault occurred in north Wembley, north-west London, the same area where engineering work was recently carried out, forcing the closure of London Euston for three consecutive weekends in August and September.
The signalling failure is not believed to be related to this work.
James Dean, chief operating officer for Network Rail’s London North Western route, said: “At 12.30pm we lost signalling in the north Wembley area.
“We have located the problem, a broken cable. We are fixing it now.
“Two train lines have reopened. We estimate full power will be back on by 3pm with train services being recovered thereafter.
“We are really sorry to all customers who have been impacted by this.
“We are working to get everyone safely on the move again as soon as possible.”
In his conference speech, Mr Corbyn spoke about the collapse of the Virgin Trains East Coast franchise and pledged that shadow transport secretary Andy McDonald “will end this shambles”.