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Parliament voted 278 to 0 in favour of keeping the top-up payment of £20 ($NZ38) week, but the vote was symbolic and does not force the government to act.
Johnson told his lawmakers on Monday to abstain in the vote, after a debate that renewed attention on whether his government is doing enough for people on low incomes after a damaging row over free school meals for needy children.
The opposition Labour Party called for the increase to the Universal Credit welfare payment to be extended beyond April, when it is due to expire.
"We all know, families are looking at us, wondering what we will do to help make getting through this crisis that little bit easier," said Labour lawmaker Jonathan Reynolds.
"What they don’t expect, is the government making it even harder."
Speaking ahead of the debate Johnson was asked four times whether the top-up would continue, but did not give a definitive answer.
"What we've said is that we will put our arms around the whole of the country."
The government says no decision has been made yet and accuses Labour of staging a political stunt with the vote.
Some members of Johnson's Conservative Party spoke out against the government, underlining dissatisfaction over ministers' handling of support for society's most vulnerable.
"People need some certainty about their family finances for the coming year," said former Conservative cabinet minister Stephen Crabb, one of six Conservatives to defy Johnson's instruction to abstain.
Britain has announced emergency help for the economy worth £280 billion, including a massive job protection scheme, and is running its largest peacetime deficit to try to soften the blow of the pandemic.
Universal Credit is Britain's main method of supporting those who are out of work, in low income jobs or eligible for welfare based on sickness or disability.
The number receiving it has almost doubled to 5.8 million from pre-pandemic levels.