Finance Minister Conor Murphy has raised doubts over whether money secured in the DUP confidence and supply deal with the Conservative party will be fully paid out.
The DUP secured a £1billion funding package for Northern Ireland for areas such as health, infrastructure and education from the then Prime Minister Theresa May in order to support her minority government.
Mr Murphy said he was attempting to “rescue” the promised money.
“That arrangement between the DUP and the Conservative party collapsed before the money was spent and the British Government is now refusing to guarantee the outstanding sums, including the money for broadband,” he said.
Around £150million was secured from the deal for ultra-fast broadband to be rolled out in rural areas.
Already the new Stormont administration is locked in negotiations to secure funding for commitments made in the New Decade, New Approach deal. Officials are compiling a costing of the pledges made by the British and Irish Governments.
There has been speculation the government has offered £2billion but with half of that coming from money that should make its way to Northern Ireland under financial rules.
The influential economist Esmond Birnie has estimated the cost of getting Northern Ireland back on its feet with enough resources to tackle the mountain of issues facing the public sector at around £5bn.
Sammy Wilson, speaking to the Belfast Telegraph, said there was no point in “moaning” about the money offered as the parties held no leverage with London with Stormont back up and running.
Finance Minister Murphy said the offer from London fell “way short” of what was needed.
“The New Decade, New Approach document was drawn up by the two governments and presented on a take-it-or-leave it basis,” he added.
“Rather than prolonging the three-year collapse of the institutions the parties rightly restored the power-sharing Executive and begun negotiations on additional funding.”
In parliament the DUP MP Gregory Campbell has asked for the government to provide a statement on the financial settlement to the Commons.
Labour leader Jeremy Corbyn said he was surprised there had not been a statement of any kind on “something as important” as the restoration of Stormont.
Prime Minister Boris Johnson and Taoiseach Leo Varadkar were in Northern Ireland at the beginning of the week to mark the restoration of devolution. Mr Johnson said it was an “historic occasion”.
First Minister Arlene Foster and deputy First Minister Michelle O’Neill have written to the Prime Minister.
Conor Murphy said they had told Mr Johnson work was ongoing over the cost of the new deal pledges.
“We want to provide accurate costs for that,” he said.
“We intend on the back of that work to engage with Treasury, to engage with the Prime Minister’s office and to engage with the Northern Ireland Office because that is where the blockage is in terms of that commitment.
“The Executive is united in terms of its approach to this.
“Once that work is complete, we will pick that up next week and we may well be over in London talking to people in the Treasury and in Downing Street.”
The DUP and the Prime Minister’s officer have been approached for comment.
Belfast Telegraph Digital