Jeremy Corbyn told Theresa May she should "lead or leave" in the first Prime Minister's Questions since her disastrous Tory conference speech.
The Labour leader criticised a "string of failures" from the Government, focusing on Universal Credit and calling for the Prime Minister to "wake up to reality" and halt its roll-out.
Universal Credit involves rolling six means-tested working-age benefits into one payment designed to make the welfare system simpler.
Mr Corbyn repeatedly criticised the process and asked Mrs May to "show some humanity" by making the UC helpline free - telling MPs it costs people 55p a minute.
"Everywhere you look it's a Government in chaos. On the most important issues facing this country it's a shambles," he said.
"Brexit negotiations - made no progress. Bombardier and other workers facing redundancy. Most working people worse off. Young people pushed into record levels of debt. A million elderly people not getting essential care. Our NHS at breaking point.
"This Government is more interested in fighting amongst themselves than in solving these problems."
Mrs May was also criticised for again refusing to say if she would back Brexit if another EU referendum happened now.
SNP's Westminster leader Ian Blackford accused Mrs May of not being "straightforward" as he challenged her on the issue.
Mrs May hit back, responding there is no second EU referendum.
She insisted Britain "will leave" the EU in March 2019 ruling out concerns the deadline could be extended.
£250 million has been allocated to help Whitehall departments prepare for Brexit - including the possibility of no deal being reached, she added.