The financial elements of any Tory deal with the Democratic Unionist Party (DUP) must be made public, shadow chancellor John McDonnell has insisted.
With talks continuing between the Conservatives and DUP over a "confidence and supply" arrangement to help get Government legislation through the Commons, Mr McDonnell has written to Chancellor Philip Hammond demanding "transparency" regarding any extra resources made available to Northern Ireland as a result of a deal.
In the letter, the shadow chancellor says: "I am writing to call on you, in the interests of transparency, to publish the financial consequences of any electoral deal reached between the Conservative Party and the Democratic Unionist Party.
"There has been speculation in the media about possible additional infrastructure and NHS spending for Northern Ireland, or reductions in Northern Ireland rates of corporation tax, VAT and/or Air Passenger Duty.
"It is essential that the details of any agreement are made public.
"Specifically, will any additional spending or tax cuts offered to Northern Ireland be offset through reductions in the Northern Ireland block grant, and if not, how will additional spending be paid for?
"Can you clarify whether any additional spending will be funded from general UK-wide taxation, or by increased borrowing, or by some other means?"
Prime Minister Theresa May began talks with the 10-strong group of DUP MPs after the disastrous Tory showing in the General Election left her eight seats shy of a majority.
The DUP has made it clear it will only cut a deal if it delivers tangible benefits for Northern Ireland in terms of jobs and investment in health and education.