Commuters are facing severe delays on the Piccadilly line caused by overrunning engineering works and a signal failure.
A large swathe of the line was suspended after engineers were late finishing works at Hyde Park Corner on Monday morning.
Services on the busy line between King's Cross and Hammersmith and then Finsbury Park to Cockfosters were halted, before the whole line eventually reopened at just before 10.15am.
Transport for London had warned the delays were likely to continue throughout the morning rush hour, hitting commuters as they began the week.
TfL urged passengers to avoid using the line if they can and added trains were likely to be very crowded and journeys heavily delayed. Tube tickets were being accepted on local buses and Great Western railway services.
Passengers complained of a "journey from hell" and a "standstill for ages" after being stuck on unmoving trains or waiting on platforms while many were caught in rainy weather.
Ian Slade said online: “No notice at Finsbury Park so now stuck at Holloway Road. Great start to first week back.”
Tasha Mathur said on Twitter: “First thing on a Monday morning and there’s already delays on the Piccadilly Line!
“Stuck at Russell Square and we can’t hear a word that the driver is saying!?”
Passenger Mal Darby added: “There are scores of people after info at Acton. 28 mins [between] trains to Uxbridge?”
A TfL spokesman told the Standard they apologise for the delay to customers' journeys and are working hard to get the line back up and running smoothly.
