The Conservatives have been accused of "giving up governing" after accepting a number of Labour amendments to the Budget in the face of a fresh DUP rebellion.
In a fresh blow to Theresa May, the Government refused to push the changes to a vote after the DUP signalled they would not support them as part of their protest against the Prime Minister's Brexit deal.
That effectively removed the Prime Minister's working majority, meaning they faced almost-certain defeat.
Shadow Chancellor John McDonnell said the move proved that the Government was "falling apart in front of us".
MPs had been expecting to vote on a string of Labour amendments to the Finance Bill on tax evasion, gaming duty and Fixed Odds Betting Terminals.
But after accepting that they were set to lose the votes, ministers indicated that they would be accepting the amendments.
John McDonnell said: "It’s absolutely staggering that the Government has accepted all Labour amendments to the Finance Bill because it couldn’t rely upon the DUP’s support.
"The Tories are in office but not in power. We’re watching a government falling apart in front of us."
One Labour source told PoliticsHome: "The Government have given up governing."
The latest blow to the fragile voting pact between the Conservatives and DUP came just 24 hours after the Government narrowly avoided defeat in a key Finance Bill vote.
The Northern Irish party are angry at the draft Brexit withdrawal agreement, which they claim effectively creates a new border between the province and the rest of the UK.
In a statement tonight, DUP deputy leader Nigel Dodds called on the Prime Minister to renegotiate the deal.
He said: "It is increasingly clear this deal does not have support necessary to pass the meaningful vote in Parliament.
"A large number of Conservatives, both Brexit supporters and ardent Remainers, are against it. Labour, SNP, Lib Dems and Plaid Cymru are against it. Unionists in Northern Ireland, and indeed unionists across the UK, are appalled at the constitutional implications of the deal.
"Therefore, rather than presenting a binary choice, it is time for the Prime Minister to work for a better deal. We recognise the genuine concerns that people have expressed about leaving the European Union on a ‘no deal’ basis. It is very clear that if we wish to avoid that scenario then the only option is to look beyond this withdrawal agreement and work for a better deal.
"A stubborn determination by the PM to pursue a binary choice of this deal or no deal is not in the country's interests.
"The confidence and supply agreement was based on shared objectives for strengthening and enhancing the Union and an exit from the European Union that benefits all parts of the United Kingdom. We have kept to our word, but even Cabinet members have found themselves having to resign because this deal does not represent those shared objectives in relation to the Union.
"The Government will require DUP support to deliver its domestic agenda. We will continue to use our influence for the good of everyone across the United Kingdom.
"If the Government can look beyond a withdrawal agreement, which is uniting people from across the political spectrum against it, and instead work towards a better deal, then an outcome can be delivered that truly works to benefit all parts of the United Kingdom."
Meanwhile, it emerged tonight that former Foreign Secretary Boris Johnson will speak at the DUP conference in Belfast on Saturday.