SNP MPs have staged a Commons takeover of the Labour opposition benches, as they sought to push their case as the "real opposition" to the Conservatives.
The nationalists said voters who did not back the Tories at the general election deserved better than Labour's refusal to oppose the Budget.
Earlier, the SNP said Labour would pay heavily for not opposing planned welfare cuts in greater numbers.
The takeover came during a debate on Tuesday evening on the Finance Bill.
The SNP occupied the frontbench normally reserved for the official opposition. Its party members also spilled onto the second and third rows.
Raising a point of order in the House of Commons chamber, SNP MP Angus MacNeil joked that, if the furniture could not be rearranged, the parties should change the seating so the "actual opposition sits in the right place".
On Monday night, plans to cut £12bn pounds from the UK welfare budget passed their first parliamentary hurdle.
The Welfare Reform and Work Bill was backed by 308 to 124 votes, with 48 of Labour's 232 MPs voting against the package.
The SNP, which voted against the legislation, said Labour's position was a ''shambles'' which would "haunt" them at the Holyrood election.
Most Labour MPs - including the party's sole Scottish member Ian Murray - abstained on the orders of acting leader Harriet Harman.
Labour leadership hopeful Andy Burnham said his party made "a mess" of its approach and was "crying out for leadership".
He said he had agreed to abstain on the key vote because he was "not prepared to split the party".
Mr Murray, the shadow Scottish secretary, said Labour would bring dozens of amendments to the legislation during its continued parliamentary journey.
He also said Scotland's SNP government must spell out how it intended to use new welfare powers being devolved to the Scottish Parliament next year.
The Edinburgh South MP, said: "What we need to be doing is working together to fight in committee on the parts of the bill that we disagree with. That is fundamentally about fairness and the impact on the sick and disabled.
Hannah Bardell, the SNP's spokeswoman on fair work and employment, said: "Labour had the perfect opportunity to join the SNP in a progressive coalition to oppose the Tories - but with some honourable exceptions they sat on their hands.
"This disgraceful stance will haunt Labour through next year's Scottish Parliament election and far beyond.
"Labour have completely abandoned any pretence of being a party of social justice and progress - just as they did when they so shamefully voted to support George Osborne's £30bn more austerity cuts."