Tube firms have been accused of passing the buck over failures which prompted the network's busiest line to close.
Work on the Northern Line is sub-contracted
London Underground's (LU) Northern Line was suspended for three days after drivers walked out when emergency brakes failed for the fifth time.
LU said it had pressed maintenance firm Tube Lines to sort the problem out. But the company in turn said it was unhappy with its sub-contractor Alstom.
London Assembly Lib Dems said the "pass the blame" game had been a "fiasco".
The Northern Line was suspended last Wednesday night, leaving the 660,000 people who use it every day seeking alternative routes home.
LU, which has overall control of the Tube network, said the fact the brakes failure had not been resolved was "completely unacceptable".
It used emergency powers to oversee work by private consortium Tube Lines, which is responsible for maintenance on part of the network.
Meanwhile Tube Lines took out an emergency directive on its sub-contractor Alstom and said it was not satisfied with its performance.
Speaking to the London Assembly's transport committee on Thursday, Lib Dem transport spokesman Geoff Pope said it had been a "fiasco".
"It is astounding that after all the chaos that has hit the Northern Line, no one has had the decency to take responsibility for the farce," he said.
Procedures 'not followed'
His comments were echoed by Rail, Maritime and Transport (RMT) union leader Bob Crow who criticised the nonsense between Tube Lines and Alstom.
And the committee's chairman, Conservative member Roger Evans said "proper control" needed to be taken over maintenance.
Tube Lines boss Terry Morgan told the committee the emergency 'trip cock' brake at the centre of last week's problems had been installed as a temporary measure, 12 years ago.
He said most of the Northern Line problems were due to the state of the fleet they had inherited.
But LU engineering director David Waboso said maintenance procedures had not been followed correctly on Northern Line trains.
Tube maintenance was privatised under the controversial public private partnership (PPP) scheme, which came into force in 2003.