A leading Unionist politician has said critics should “grow up” and accept the idea that the Democratic Unionist Party could demand curbs on rival Sinn Fein’s funding as a price for propping up the Conservative government.

The controversial demands, understood to be among a series of requests DUP leader Arlene Foster will make from Theresa May in talks over a "confidence and supply" arrangement, would put curbs on foreign donations to political parties, and would limit Sinn Fein’s sizeable donations from Irish Americans.

David Trimble, the former First Minister of Ireland who helped broker the Good Friday Agreement while leader of the more moderate Ulster Unionist Party, said of the requests: "If it is a matter of bringing the law into line with elsewhere, then people should be grown up about it."

Lord Trimble, who won the Nobel Peace Prize in the late 90s for his work on the Good Friday Agreement and who now sits as a Conservative peer, also dismissed as "scare-mongering" the idea that a DUP deal with the Conservatives might put the agreement in jeopardy.

“There is no connection between the agreement, between the European Union, between the talks and all the rest of it,” Mr Trimble told the Today Programme. “People are just trying to grab this as a stick to beat the government with and I think it’s quite silly.”

Tony Blair brought in restrictions on foreign funding for political parties, but deliberately excluded Northern Ireland from the measures. Sinn Fein continue to receive millions of euros each year from US backers. Asked if any concession by the Conservatives that favoured the DUP over Sinn Fein would threaten the British government’s position as an ‘honest broker’ between the two, Lord Trimble said: “What is at issue here is bringing the law in Northern Ireland into line with the rest of the country.

"If it is a matter of bringing the law into line with elsewhere, then people should be grown up about it."

The DUP is understood to have a list of demands that is 45 points long, originally drawn up for the 2015 election, when it thought it might hold the balance of power. It also includes removing funding from MPs who abstain their seats in Parliament. Sinn Fein has never taken its seats in Westminster, but funds local party offices using the expenses it receives from Westminster. It currently has seven elected MPs.