Protracted power talks between Theresa May and Arlene Foster are expected to resume at Downing Street with the DUP leader raising prospects that a deal is finally set to be done.
Lord Patten, a former party chairman, called the DUP "toxic" and warned that any agreement would look as if the Conservatives have become "nasty" again if it was too favourable to Northern Ireland.
Foster's party had demanded tangible benefits in terms of jobs and investment for Northern Ireland before she would agree to support May's government.
Parties have raised concerns that the ongoing DUP-Tory talks are undermining the negotiations on restoring devolution at Stormont.
'We very much want to see that protected and enhanced and we also share the desire to ensure a strong government, able to put through its programme and provide for issues like the Brexit negotiations, but also national security issues.
She added that the funding would "address the unique circumstances" of Northern Ireland and the impact on its people.More news: SpaceX set to launch satellites from California air base
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'So the agreement we have come to is a very, very good one, and look forward to working with you'. They smiled and joked as negotiators from both sides, the DUP's Jeffrey Donaldson and the Conservatives' Gavin Williamson signed the deal.
A deal would allow May to pass legislation with the backing of the DUP in the 650-seat parliament, and stay in power as she attempts to negotiate Britain's exit from the European Union.
The leader of a Northern Ireland-based party is in London to finalize an agreement with Prime Minister Theresa May's Conservative-led government to support it in a crucial vote on the government's legislative package later this week.
The DUP also secured more than $1 billion in economic assistance for Northern Ireland.
With the deal appearing to be edging closer to completion over lengthy talks, it was still facing criticism even within the Conservative party. "I mean, tell that to the Marines, Northern Ireland has got a lot of public spending over the years".
Lord Patten suggested yesterday that "every vote" from the DUP would cost the country money and suggested voters in the other parts of the United Kingdom would be angry that Ulster was getting special treatment.
Labour Welsh first minister Carwyn Jones said: "Today's deal represents a straight bung to keep a weak prime minister and a faltering government in office". "Cuts to vital public services must be halted right across the United Kingdom, not just in Northern Ireland". Where is the money for the Tory-DUP deal coming from? They say it jeopardizes the government's pledge to be a neutral arbiter as part of the Good Friday agreement, which in 1998 brought peace to Northern Ireland after decades of sectarian strife.