The Welsh first minister Carwyn Jones described the deal as a "straight bung to keep a weak prime minister and a faltering government in office", while Scotland's first minister Nicola Sturgeon said it was "the worst kind of pork barrel politics".
The Conservative Party led by British Prime Minister Theresa May on Monday signed an agreement with Northern Ireland based Democratic Unionist Party to provide Confidence and Supply in the Parliament.
The Conservatives need the support of DUP's 10 MPs after managing to get 317 seats in the 650-seat parliament.
The fact that the deal commits a substantial amount of extra money to Northern Ireland for help with infrastructure, education and health services is likely to provoke protest from other regions that are also seeking more funding from the central government for a variety of programs.
Prime Minister Theresa May and DUP leader Arlene Foster today finalised an agreement that will see DUP MPs back the Tories in key Commons votes.
Discussions between the Conservatives and the DUP began immediately after the election, stirring up further resentment against the embattled May who was left weakened by the embarrassing political setback. But if they calculate in two years-time that the Tories still want to avoid an election at nearly any cost, the price for their support will increase.More news: Air bag recalls, lawsuits lead Takata to file for bankruptcy
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The DUP has backed a deal to support the minority Conservative Government.
It is not known yet what exactly the terms of the agreement are but the BBC reports that there has been £1 billion extra funding for Northern Ireland over the next two years. Foster said the details of the deal with Conservatives will be published.
In a later statement, Sturgeon said she and Jones would be seeking "urgent discussions" with the United Kingdom government about funding and said the deal "shredded the last vestiges of credibility of this weakened Prime Minister".
The prospect of a deal with the ultra-conservative DUP has caused consternation in Britain since the party opposes gay marriage and abortion.
Her Majesty's government will continue to do everything we can to work with the parties in Northern Ireland, alongside the Irish government, to bring back a strong voice at Stormont for a positive future for everyone in Northern Ireland.
- Recognising the longstanding focus on securing a modern, sustainable health service in Northern Ireland, the United Kingdom government will allocate 100 million pounds per year for two years to support health service transformation.
Downing Street has said that as the allocation is being made as part of the block grant to Northern Ireland, there will be no consequentials through the Barnett formula, the mechanism used to distribute Treasury funds to the devolved nations.