FILE PHOTO: Britain's Prime Minister Theresa May leaves 10 Downing Street in London, September 6, 2017. REUTERS/Toby Melville/File Photo

LONDON (Reuters) - British Prime Minister Theresa May must seek parliamentary approval for a billion-pound deal with a Northern Irish party that propped up her government after an inconclusive election, a legal campaigner quoted government lawyers as saying on Monday.

After losing her majority at the June 8 election, May’s Conservative Party secured the support of the small Democratic Unionist Party which allowed her to form a minority government. Northern Ireland would get 1 billion pounds ($1.3 billion) extra funding as part of the deal, the government said at the time. [nL8N1JN0LL]

But, citing correspondence with government lawyers, campaigner Gina Miller, who defeated ministers in an earlier high-profile legal case over the process for triggering Britain’s exit from the European Union, said the deal could not be executed without parliamentary approval.

Alongside a statement condemning the government for not making the need for parliamentary approval public, Miller released a letter from the government’s legal department.

“The agreement does not, and could not, involve the Government providing or committing itself to any provision of additional funds to Northern Ireland which would not be authorised under standard procedures, including the consent of Parliament,” the letter said.

A spokesman from May’s office said all government spending required parliamentary authorisation, and that its focus in Northern Ireland was on ending a political stalemate that has left it without a regional government for eight months.

Any parliamentary vote would be expected to pass with the support of Conservative and DUP lawmakers, but could invite further unwelcome scrutiny of a deal which has been heavily criticised by political opponents.

The opposition Labour Party described it as a “bribe” and said the government needed to be clear about how it would be paid for.

In January, Miller successfully challenged the government’s plan to begin EU divorce proceedings without first seeking parliamentary approval. After a Supreme Court ruling sided with Miller in that case, May was forced to pass legislation through parliament.