First Minister Alex Salmond yesterday claimed that the Labour Party north and south of the border is guilty of a "systemic" abuse of the electoral law they introduced.

Mr Salmond's comments came as Wendy Alexander spoke publicly for the first time in nearly six weeks on the illegal donations row dogging her leadership of the party in Scotland.

Pressure was also building on Peter Hain, the Work and Pensions Secretary, over his failure to report £103,000 of donations to his campaign to become deputy leader of the party nationally.

The Electoral Commission is conducting inquiries into both matters, while Mr Hain is also facing the prospect of an investigation by Westminster's powerful Parliamentary Commissioner for Standards.

Appearing on the BBC's Politics Show yesterday, the First Minister said the Electoral Commission must protect its "credibility" by taking action.

He said: "I think the problem for the Labour Party is this: it does look like there's a systemic failure in the Labour Party to observe the law that they introduced.

"Whether it's the Labour Party, whether it's the Labour Party in Scotland or whether it's Peter Hain, there's at least a prima facie case where arrangements were made or companies were invented to circumvent the law.

"This is really now in my view a test for the Electoral Commission.

"If this is systemic, as it looks, then they cannot in terms of the credibility of the Electoral Commission continue to allow the Labour Party get away with this sort of thing."

Ms Alexander yesterday said she was "confident" she would be cleared by the commission, but Mr Hain added nothing to the public statement he made on Saturday in which he dismissed calls for his resignation.

"The notion that there was some attempt by me to hide anything is absurd," he said.

"As with all candidates, money was raised by my campaign team. All those who contributed are people and organisations who are eligible and legally entitled to do so."

But critics said there were still many unanswered questions, particularly surrounding the Progressive Policies Forum, a mysterious think tank via which donations were channelled to Mr Hain's fund.

Tory leader David Cameron suggested the body could have been a "front" and said Prime Minister Gordon Brown, who has given Mr Hain his backing, was "dithering" over the matter.

He said: "If I was in the Prime Minister's shoes I would say to Peter Hain, look, you've got to get out there, you have got to explain yourself, you've got to answer all these questions. And if you can do that then maybe your job is safe, but if you can't then you will have to go'.

"I think that's where we ought to be. Instead, I sense that Gordon Brown is dithering over the issue."

Labour colleagues rallied round Mr Hain, who is also Welsh Secretary.

Schools minister Jim Knight acknowledged that it was embarrassing for Labour to be "tripping over our own rules" but insisted Mr Hain's problems stemmed from "an administrative problem".

Foreign Office minister Lord Malloch-Brown also blamed the controversy on "administrative shortcomings".

Labour MP Don Touhig said: "Peter Hain has admitted that it's a total foul up.

"He's mortified and regrets what's happened.

"He has been totally open and transparent. It's Peter Hain who has put all this information into the public area."