Humza Yousaf said he was shown a police warrant to seize items from the party, which included the vehicle.

The motorhome was seized from outside a property in Dunfermline last week.

Party sources are reported to have said it was intended to be used as a "campaign battle bus" ahead of the last Holyrood election in 2021.

They told the Daily Record that it would have acted as a "mobile campaign room" if Covid restrictions prevented other forms of mixing, but was never used.

Mr Yousaf was asked during a visit to a Glasgow nursery school when he first learned that the party had bought the Niesmann + Bischoff vehicle, which can retail for more than £100,000.

He replied: "Shortly after I became leader of the party".

The first minister said: "The police of course give us a warrant for items that they are looking to take in their possession.

"I can't go into the detail of that but of course the police have done the responsible thing and I as leader have seen the warrant in terms of the items that they've confiscated, including the motorhome that you referenced."

The Mail on Sunday reported at the weekend that the vehicle had been parked outside the home of Peter Murrell's 92-year-old mother since January 2021. Mr Murrell is married to Nicola Sturgeon, and was until recently the SNP's chief executive.

It was said to have been taken away on the same day that officers searched Ms Sturgeon and Mr Murrell's home in Glasgow, and the SNP's headquarters in Edinburgh. Mr Murrell was arrested before later being released without charge.

Campervans similar to the one seized by police can retail for more than £100,000

Officers are investigating the SNP's finances in response to complaints about how the party spent more than £600,000 of donations that it had received from activists.

Mr Yousaf said the public had "very reasonable" questions to ask regarding the issue of transparency within the SNP.

It has been revealed that the SNP has been without auditors since September. Accountants Johnston Carmichael, which audited its accounts for more than a decade, said the decision to no longer work with the party was taken after a review of its clients.

Mr Yousaf said he had not been aware of the issue until he became leader, adding that "it would have been helpful to have known beforehand" and that "there should have been more transparency around the party finances".

He said he was now committed to finding replacement auditors for the party as soon as possible.

The first minister was speaking the day after the Scottish government confirmed it would be launching a legal challenge to the UK government's block on its gender recognition reforms.

Mr Yousaf said he did not "know the full costs" that would be involved in taking legal action, but insisted that "it's an important principle".

He said: "Spending taxpayers' money on defending the will of the Scottish Parliament, on defending devolution, for me that's important."

He said he would launch the challenge even if it was a bill he "fundamentally disagreed" with, claiming that if he did not do so then the UK government would "veto legislation after legislation" passed at Holyrood.

However, former Supreme Court judge Lord Sumption told the BBC that the Scottish government's position was "weak" and the legal challenge would be "very difficult".

The case for judicial review will initially be heard in the Court of Session in Edinburgh, but is widely expected to end up in the UK Supreme Court for a final decision.

Lord Sumption told the BBC Radio's Good Morning Scotland programme: "Section 35 empowers the UK government to stop a Scottish bill becoming law if it modifies the law relating to a matter reserved to Westminster in a way that adversely affects how the law works.

"One of those matters is equal opportunities, and what the UK government says is the Scottish bill modifies the law relating to equal opportunities in a way that adversely affects how it works.

"So if you think about it, the result will be that some UK citizens, if this bill comes into force, will have a different legal gender in different parts of the UK depending on where they happen to be."

Asked if he would resign as first minister if the legal challenge was unsuccessful, Mr Yousaf replied: "No".