Liberal Democrat leader Sir Vince Cable has said his party has "nothing to apologise for" after questions were raised about election spending.
A second Liberal Democrat MP has denied wrongdoing over claims about the way campaign spending was accounted for.
Christine Jardine, who took Edinburgh West from the SNP in June's election, described the claims as a "smear".
It follows questions about the expenses of Liberal Democrat deputy leader Jo Swinson in East Dunbartonshire.
The Electoral Commission strictly limits the amount a candidate can spend to be elected to a Westminster seat to ensure there is a level playing field.
According to The Herald newspaper, Ms Jardine failed to include £3,000 in her total campaign costs submitted to the Electoral Commission. The paper said that if the costs had been included, it would have taken her over the spending limit.
Ms Jardine, however, has insisted the spending was on the national campaign, and did not need to be included because it did not highlight her as the local candidate.
Sir Vince Cable, the UK party leader, was questioned on the issue during a visit to Edinburgh to meet party activists.
He said: "My understanding is it's absolutely completely above reproach, that there's absolutely no question of any impropriety and what's happened is it's a complex process apportioning costs, but the party has followed advice.
"There's no question of anything wrong whatsoever, nothing to apologise for. As far as I'm aware no official complaints have been made and from what I understand there's no basis for making them."
Christine Jardine won the Edinburgh West seat by 2,988 votes over the SNP's Toni Giugliano.
She told the BBC's Good Morning Scotland programme: "If it had been local expenditure, it would have been included as local expenditure.
"It was national expenditure and therefore it was counted as national expenditure."
Ms Jardine described the story as "weak" and denied playing "fast and loose" with the rule book, saying: "No, no we're not, we're following the rules to the letter.
"That is kind of like saying I spent x-number of pounds on my car and x-number of pounds on my house and then trying to say that everything was spent on your house.
"No. The money which was spent on the national campaign was spent on the national campaign and the money which was spent on the local campaign was accounted for in the local campaign.
"This is nothing more than an exercise in reputational damage by the SNP because they lost the seat."
On Wednesday, it emerged that Ms Swinson's spending came in £210 below the legal limit.
She took the East Dunbartonshire seat from the SNP with a 5,339 majority amid questions over £7,000 of expenses, which she said were only used to promote the national party.
The Electoral Commission said it had not received a complaint about either candidate.
A spokeswoman said: "General election candidates or their agents must submit campaign spending returns to their local authority.
"Any investigations into alleged breaches of candidate spending rules would be a matter for the police."
Police Scotland confirmed that they had not received any complaints in relation to the matter.
In June last year, the Lib Dems' general election campaign director Alex Cole-Hamilton was reported to prosecutors over an allegation that he may have breached the legal spending cap regarding the Holyrood election campaign. The party denies any wrongdoing.
SNP MP Pete Wishart said there was an "extremely worrying pattern" emerging.
He said: "Vince Cable needs to get a grip of his party and explain just how widespread these practices are.
"The Lib Dems must start being transparent about what they spent in constituencies across Scotland or else we've got an emerging election expenses scandal on our hands."
He added: "Edinburgh West is where the Lib Dems faced a police probe into their expenditure during after last year's Holyrood election.
"They've clearly not learnt any lessons from that experience.
"But they now have the chance to come clean and provide the evidence of the vanishing leaflets and fess up to what appears to be creative allocation of local and national spending."