Tube passengers suffered fresh disruption today on a London Underground line which was shut during last night's rush hour, trapping commuters for over an hour.
Services on the Jubilee Line were affected again this morning by a signal failure, leading to "severe" delays and fuelling calls for London's Mayor Boris Johnson to take action.
Commuters on the same line were trapped in crammed underground trains last night - the hottest day of the year.
Some passengers had to endure sweltering temperatures for over an hour before being evacuated through tunnels after a major power failure crippled the line.
The entire line was shut shortly after 7pm yesterday following technical problems, leaving five trains stranded between Kilburn and Canary Wharf.
Underground staff were forced to evacuate thousands of commuters along tracks and through tunnels, while teams of paramedics were sent to meet them over fears of dehydration.
A Transport for London spokesman said: "We would like to apologise to passengers for the disruption to services caused by a power failure on the Jubilee Line.
"Following a report of power failure at Canning Town, the Jubilee was suspended on Tuesday evening.
"Five trains were stalled between Kilburn and Canary Wharf.
"Local ambulance services were dispatched as a matter of course and staff worked to detrain all passengers as quickly as possible.
"No passengers required medical assistance."
Gerry Doherty, leader of the Transport Salaried Staffs Association, said today: "It is high time that Boris Johnson got a grip on the Tube service which has frankly been appalling for many months.
"He keeps claiming that these failings are temporary and everything will be alright on the night when the Olympics gets under way next summer.
"With 500,000 extra visitors expected, he cannot afford to get it wrong. Talk is cheap - we want action now."
Many passengers took to social networking sites to vent their anger at TfL. Glamour magazine editor Jo Elvin was one of those stuck on the Jubilee line.
She wrote on Twitter: "I have just been trapped in an overheated Tube for nearly 30 mins. They didn't know how to get us out.
"So angry and disturbed. That line is a constant joke. That was genuinely alarming, was a bloody oven in there!
"It's just not acceptable to hear announcements such as 'we don't know how to open the doors'. Reassuring, eh? Nice touch too, making us still fish out our tickets for the barriers."
Another Twitter user wrote: "My girlfriend had to walk 20 minutes through a tunnel on the Jubilee line, with no water tonight. This is how we treat commuters - it's sick."
Ken Livingstone, Labour's London Mayoral candidate said: "The Olympics are little over a year away, fares are soaring over inflation and yet delays and chaos on the Tube are unresolved.
"It has become a fiasco, an embarrassment to a world city."
Meanwhile, LU today reported it carried a record 1.1 billion passengers in the past year. During the year ending March 31, the Tube saw about 42 million more passenger journeys than the previous year.
The network also broke its record for the number of passengers carried over a four-week period - topping 90.6 million in the four weeks leading up to Christmas.
LU said it had seen a rise in passenger numbers of 14% in seven years and 40% in 15 years.
Rail Maritime and Transport union leader Bob Crow said: "Two weeks ago the Mayor promised Londoners an end to the chaos on the Jubilee Line - last night and this morning we have seen that the crisis has actually got worse.
"It's time to stop the lies and broken promises and to start working with the unions to put an end to this misery and that means tackling the in-built faults at the heart of the Jubilee operating system and taking action against those who bought and sold us this billion pound pig-in-a-poke.
"RMT members have warned repeatedly that privatisation has left us with a Jubilee Line system that isn't fit for purpose and the misery will continue until that is tackled. Last night also showed why we need platform staff to assist passengers in a breakdown situation and it is time for the cuts to those staff to be stopped."
A TfL spokesman said: "We apologise to customers for today's part suspension of the Jubilee Line between Willesden Green and London Bridge. This is due to a signal failure at Baker Street and is unrelated to last night's suspension, which was a power supply issue
"The part suspension has been put in place to ensure we can continue to run reliable services at the busy ends of the line. Alternative Tube services are available in central London and there is a good service running on other lines.
"We will be refunding customers affected by this morning's Jubilee line issues, as we are last night's."