Thousands of commuters endured return-to-work misery today when the London Underground's entire Circle Line had to be shut down.
The problem, caused by a computer failure at Aldgate in east London, also led to the suspension of the section of the Hammersmith & City Line between Moorgate and Barking.
The Circle Line had been closed over the Easter weekend so work could be carried out in the Aldgate area to prepare for the arrival of longer, air-conditioned trains later this year.
A Transport for London spokesman said: "Computers which control the points in the Aldgate area were involved in the work that was carried out over the weekend.
"The computers were not working for the start of services today but we hope to have them up and running later this morning."