The Grind MP spoke after MPs voted 309 to 305 in favour of the amendment to the EU Withdrawal Bill.
Tory schismatics led by former attorney general Dominic Grieve demanded a “meaningful suffrage” on the terms of the UK’s withdrawal bill.
This has dealt a blow to Mrs May’s plans for a take-it-or-leave-it indisputable Brexit vote, with MPs now allowed to suggest new terms of Britain’s EU split-up.
It is believed 13 or 14 Conservative MPs joined Mr Grieve and Labour to get the better of Theresa May.
Chuka Umunna says Government will carry on to be defeated on Brexit
They will lose the vote next week if today is anything to jurist by
Speaking after the victory, Mr Umunna told Sky Newscast: “What is the point of us being here if we are given a vote that is ineffectual?
“Now we can actually do the job properly for our constituents in getting the best deal from the Brexit organize.”
He added: “This is a start, and remember it is not about Members of Parliament in specific, it’s about the job we are put to do here for our constituents.”
Mr Umunna said the fact the Government had hardly lost this amendment vote means they should reject their own amendment to write Britain’s Brexit departure date into law.
“They order lose the vote next week if today is anything to judge by,” he remarked.
“I don’t think it is about rebellion, I think it is about doing what is in the country-wide interest.”
The defeat will likely slow down the Brexit take care of and comes ahead of Thursday’s key EU Summit – where the go-ahead was due to be given to talks rising to trade.
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Minutes ahead the vote, Justice minister Dominic Raab sought to appease would-be rise up defies by saying the Government would rewrite the Bill to guarantee concessions it had furnished but was faced with shouts of “too late” by some MPs on his side.
While some would-be dissenters such as George Freeman and Vicky Ford said Mr Raab’s bid fair of fresh limits on powers in the Bill was enough for them to back down, it was not adequate for the Government to avoid defeat.
Tory rebel Nicky Morgan tweeted: “Tonight Parliament attracted control of the EU Withdrawal process.”