http://news.bbc.co.uk/1/hi/wales/6394985.stm
Rail engineers have worked overnight to try to repair a signalling fault that caused hundreds of football fans to miss the Carling Cup final kick-off.
Fans of both teams heading to and from the Cardiff's Millennium Stadium were affected by the delays.
Queues outside Cardiff Central train station took more than four hours to clear after the match.
Network Rail has apologised for the delays, which have continued while the fault is repaired.
Monday's First Great Western 0715 London Paddington to Cardiff and 0955 Cardiff to London services have been cancelled and other services are facing delays of up to half an hour until midday.
In addition, services from Portsmouth to Cardiff are terminating at Bristol before returning.
The disruption is a continuation of the delays which saw an estimated 2,000 football fans miss the start of Sunday's Carling Cup final between Chelsea and Arsenal in Cardiff.
Police said the atmosphere among football fans before and after Sunday's match was largely good natured, however many complained they were not given enough information.
Many more supporters spent much of last night trying to get home after the match.
A serious electrical problem was identified at Newport on Sunday morning, just hours before thousands of supporters were due to travel on the line.
It meant that many spent up to three hours between Bristol and Cardiff, forcing them to take their seats midway through the first half.
Fans heading back to London said it had ruined what may have been the last time they visit Cardiff for a major football cup final.
Although some trains were up to 90 minutes late for the game, football officials ruled the match should still start on time.
British Transport Police said the signalling problem was caused by an isolated electrical problem in the cables at Newport.
Network Rail spokesman Ben Herbert apologised for the delays, which he said had been caused by a "fairly serious" but unforeseen signalling problem.
He told BBC Radio Wales: "We can appreciate it did cause pretty major disruption for a lot of people yesterday and this morning.
"If we had known about it, we would have put arrangements in place, worked with the train operators, to make people aware a lot earlier.
"Unfortunately it is one of these things we could not have foreseen. It was very unfortunate it did coincide with that very big match at the Millennium Stadium."
The match, which ended in a 2-1 victory for Chelsea, was the seventh Carling Cup final to have been held in south Wales during the rebuilding of English football's traditional home, Wembley, in north London.
Football's showpiece games are due to return to Wembley, beginning with the FA Cup Final in May.