All eyes are on the government’s alliance with the Democratic Unionist Party, which is threatening to break up over Brexit.
The confidence and supply deal was signed for £1.5bn last June – weeks after the Conservatives lost their majority in a snap general election.
But it is beginning to unravel as the Northern Irish party flexes its muscles over a draft divorce deal from the EU.
All 10 of the DUP’s MPs abstained on amendments to the finance bill, which will introduce tax and duty changes announced in the budget.
With the agreement now in question, Sky News unpicks exactly what the two sides promised:
:: What is a confidence and supply deal?
A confidence and supply deal is set up when a government needs the support of another small party to function.
Simply, it is an agreement for the second party to uphold “confidence” in the prime minister by “supplying” them with votes on key laws.
The current arrangement was set up in June 2017 when Theresa May called a snap election but ended up losing her majority.
With 318 MPs – eight less than needed to win a majority in the Commons – the prime minister sought the help of the DUP’s 10 MPs to take her over the line.
It took over two weeks to broker, with the Conservatives promising £1bn in “new money” for Northern Ireland and greater flexibility for the DUP over £500m already allocated to the country.
The three-page document was supposed to “deliver a stable government in the UK’s national interest”.
:: How long did the DUP agree to support the government?
First and foremost it agreed to a timeframe.
The agreement tied it to supporting the government “for the duration of this parliament”.
Parliament can be dissolved if two-thirds of MPs vote for it, triggering a general election, but otherwise the expected end of the parliamentary term is five years from the previous election.
That would have in principle bound the DUP to support the government until 8 June 2022, at the latest.
The terms of the agreement can only be changed at the “mutual consent” of both parties.
:: What did the DUP agree to back the government on?
The deal says the DUP must support the Conservatives on:
- All motions of confidence
- The Queen’s Speech
- The budget
- Finance bills
- Money bills
- Supply and appropriation legislation
Essentially anything that involves spending taxpayers’ money.
There is another crucial and loosely-worded condition:
“The DUP also agrees to support the government on legislation pertaining to the UK’s exit from the EU and legislation pertaining to national security.”
Support on other matters is agreed on “a case-by-case basis”.
:: And what did the government agree to do?
Mrs May signed up to a raft of policies to keep the DUP on-side.
They include no changes to the pensions triple lock, keeping the winter fuel payment universal and spending 2% of GDP on defence.
It also promised to “adhere fully” to its commitment defined in the Good Friday Agreement.
And it promised to “support close co-operation” with the Irish government.