THERESA May has been forced to defend the Scottish Conservatives against claims they have benefited from hundreds of thousands of pounds of so-called “dark money”.

The Prime Minister was quizzed about the obscure Scottish Unionist Association Trust (SUAT), which has donated almost £319,000 to dozens of Scottish Tory branches since 2001.

At Prime Minister’s Questions, SNP Westminster leader Ian Blackford urged Mrs May to launch an investigation into the secretive group.

The exchange prompted an unprecented statement from the SUAT.

According to Westminster’s register of members’ interest, the SUAT gave £7500 to both Banff & Buchan MP David Duguid and Moray MP Douglas Ross last year.

The SUAT also donated up to £5000 to Jackson Carlaw in 2006 and 2007 while he was a senior member of the Scottish Tories, but before he was elected an MSP.

However there is no public record of its board, only an office address in Mosspark, Glasgow, which has long been used by the Glasgow Tories.

Mr Blackford said there was “no information” about the trust's management.

He said: "The Conservatives are systematically shielding their donations from public scrutiny, Jackson Carlaw MSP for Eastwood, (David Duguid) and (Ross Thomson) have all accepted donations from the Scottish Unionist Association Trust.

“The trust has donated £319,000 to the Scottish Conservatives, yet there is no information available about who the people are who currently manage the trust, no public accounts indicate who its donors are or what assets it holds.

"I'm now giving the Prime Minister the chance to tell us what checks the Scottish Tory party had in place before accepting such large donations and will she investigate the links between the Conservative Party and the trust and promise to publish a list of all donations and donors?”

Mrs May responded: "I can tell him that all donations to the Scottish Conservative Party are accepted and declared in accordance with the law and the Scottish Conservative Party works with the Electoral Commission to make sure that that is all done properly."

The Scottish Conservatives refused to say who was on the board of the SUAT, or whether the party was satisfied the SUAT abided by electoral law.

A spokesman said: “SUAT are a separate organisation, so all questions will have to go to them.”

Asked for a way to contact the secretive outfit, he said: “I’m not a phone book. If you want to speak to them, you’ll have to find a way yourself.”

Speaking after PMQs, Mr Blackford said: "The Prime Minister cannot dismiss the scandal that the Scottish Tories have found themselves in regarding these dodgy donations.

“We need absolute transparency and someone must be held accountable - whether it is the Vote Leave campaign or the funding of the Scottish Conservative Party, our democracy cannot be bought. 

"I gave the Prime Minister the chance to tell us what checks the Scottish Tory party had in place before accepting such large donations and ask, will she investigate the links between her Party and the trust with a promise to publish all donors and donations?"

In his financial report to the Scottish Tories’ spring conference - published before the event was cancelled by bad weather - party treasurer Bryan Johnston thanked the SUAT.

He said: “The Party relies on the generosity of its supporters and we really do appreciate each and every donation we receive whether it is donated locally to a branch, an association or to a national appeal.

"I would like to especially thank the Trustees of the Scottish Unionist Association Trust for the Trust’s considerable financial support in 2017, particularly with support at the General Election."

The SUAT was also due to sponsor two receptions at the conference - the Conference Convenor’s Reception and the Scottish Conservatives Candidates’ Reception.

The SUAT later released a statement on behalf of its trustees.

It said: "The Trust was formed in 1968 from assets of the (then) Scottish Unionist Association, primarily sales of property assets. It invests those assets and makes the proceeds available to further the aims of the Scottish Conservative and Unionist Party. All UK taxation liabilities have been and continue to be met in full.

"The address for the Trust is 570 Mosspark Boulevard, Glasgow G52 1SD. Previous addresses may have been used for correspondence in the past, and have been changed as trustees have changed over time.

"Current trustees are all resident in Scotland, as has been the case for all previous trustees. They are: Robert Millar-Bakewell (Chairman), Kim Donald, Patricia McPhee, Sheila Fulton, John Duncan, Peter Duncan, Frank Spencer Nairn."

In relation to reports the Electoral Commission was investigating the SUAT's status, a spokesman for the Trust said: "We are in dialogue with the Electoral Commission and it would be inappropriate to say more whilst that dialogue continues."