A huge signal failure this morning meant the Piccadilly and District lines were completely suspended.
As some commuters complained of being 'underground for an hour' Transport for London said there was no service while the problem was fixed.
The Hammersmith & City line has also been hit with severe delays between Liverpool Street and Hammersmith caused by the signal failure.
There is no service between Liverpool Street and Barking.
TfL are advising people to take alternative routes with tickets being accepted on other lines and bus services.
The Piccadilly Line was partially re-opened at around 10am but there was still no service from Hyde Park Corner to all Heathrow terminals and Uxbridge.
There are severe delays from Hyde Park Corner to Cockfosters.