Peter Murrell, once one of the most powerful people in British politics, faces a long prison sentence after he admitted to stealing more than £400,000 from the Scottish National party to fund a lavish personal lifestyle.

The former SNP chief executive Murrell admitted on Monday he used the stolen money between 2010 and 2022 to buy items including a luxury motor home, a Jaguar SUV and a VW Golf, boutique cosmetics, iPads and a Lalique Feuilles salt and pepper set worth £2,618.

The full details of his embezzlement emerged in the high court in Edinburgh on Monday after he reached a deal with prosecutors brokered over recent weeks to plead guilty to embezzling £400,310.65, avoiding a lengthy trial.

Lord Young said Murrell, who was married at the time of the thefts to Nicola Sturgeon, the former SNP leader and first minister, was guilty of a “gross breach of trust”.

Murrell, dressed in a dark blue suit and black tie, was led away in handcuffs by a court security officer after being remanded in custody. He now faces a lengthy term in jail at his sentencing on 23 June.

Under pressure from the SNP’s political opponents, Sturgeon issued a statement on Instagram again denying she had any knowledge or suspicion of her former husband’s thefts. “I am utterly appalled that he did so and cannot begin to understand why,” she said. “These are not my crimes. I was misled just as others were.

“To be deceived and let down by a husband I loved and trusted has caused me acute pain. Why he acted as he did is, and always will be, beyond my comprehension.”

John Swinney, the current SNP leader and once one of Sturgeon’s most trusted advisers, also said he felt utterly betrayed by Murrell’s behaviour. Swinney was party leader when Murrell was appointed chief executive in 2001.

During a press conference called to respond to Murrell’s deal, at one stage Swinney fought back tears, looked at the floor and gripped the podium tightly with both hands when was asked how he felt personally.

“I’m gutted by this today,” he said, acknowledging he was sorry for the ordinary SNP members on modest incomes who had donated or raised money, only for it to be stolen by Murrell. “This is a tough day. So the level of personal horror, betrayal, that I feel is difficult to properly convey to you.”

Swinney sidestepped questions about why Sturgeon appeared unconcerned about the luxury goods Murrell was bringing home or whether the officials who were castigated for initially raising the alarm about party accounts were owed an apology.

He said Murrell was able to steal from party members for so long because noone could conceive that someone in his position would do so. The party’s financial controls had since been significantly tightened, he added.

Russell Findlay, the Scottish Conservative leader, and Jackie Baillie, Scottish Labour’s deputy leader, said Sturgeon and Swinney’s denials that they had suspicions of such a “large-scale fraud” were not credible.

Baillie said: “Swinney should do the right thing and provide compensation to all those who handed over their money to the SNP.”

In a statement issued through her lawyer, Sturgeon said she had no idea Murrell had bought a camper van until the police investigation, and did not know of the luxury watches or games consoles.

“In respect of any items I was aware of Peter having purchased, I had no reason to doubt that he had used his own money,” she said.

“We were both earning high salaries and, due to the responsibilities of my job, rarely socialised or went on holidays. We had separate bank accounts and I had no access to his financial records.”

The chief executive of the SNP for 22 years, Murrell played a pivotal role in engineering the SNP’s first ever victory in the 2007 Holyrood elections and its subsequent landslide win in 2011, which triggered the decision to hold the Scottish independence referendum three years later.

He was married to Nicola Sturgeon at the time, and they became the most powerful couple in British politics when she succeeded Alex Salmond as SNP leader and first minister in 2014, overseeing an unbroken run of SNP election victories.

Yet the lengthy indictment, which included a 119-page list of all the items he bought using the SNP’s money, disclosed that for much of that time he was pilfering the SNP’s accounts to acquire a remarkable series of luxury goods, while earning £107,000 as party chief executive.

The indictment noted that in addition to the £124,000 motorhome, which he left parked in his mother’s driveway in Fife, and the Jaguar I-Pace, he bought gardening equipment for the home he shared with Sturgeon, a £1,3000 Miele coffee machine for their home, a telescope, a Sony PlayStation, Fortnum & Mason hampers and several Montblanc fountain pens.

The charge said he submitted false invoices, used the party’s credit cards, falsified the party’s accounts and in some cases claimed they were legitimate expenses to cover up his embezzlement. Several times he used credit cards taken out in the names of SNP staff who worked for him.

After his guilty plea, Stuart Houston, the assistant chief constable in overall charge of Police Scotland’s investigation, known as Operation Branchform, said the investigation had been “extremely complex” as Murrell had worked hard to cover his tracks.

“Peter Murrell has shown utter contempt for the high public trust placed in him,” Houston said. “He abused his privileged position with access to Scottish National party funds to divert cash into his own accounts and bankroll the lavish lifestyle he craved but could not afford.”

Operation Branchform was launched in July 2021 after the police received a series of complaints about the SNP’s finances, with concerns first raised in late 2020.

During a turbulent period inside the party, party members serving on its finance and audit committee resigned, as did the party’s treasurer, Douglas Chapman MP, saying they had been denied access to the SNP’s accounts.

Attention focused on the absence of more than £660,000 in donations raised by the SNP for pro-independence campaigns in the party’s accounts; those campaigns were never staged. In September 2022, the party’s longstanding auditors, Johnston Carmichael, resigned.

While the party’s then treasurer, Colin Beattie, acknowledged there were concerns about transparency, Sturgeon repeatedly insisted the party’s overall financial affairs were in order.

Murrell was arrested at the home he then shared with Sturgeon on 5 April 2023, and the motorhome seized outside his mother’s home in Fife, while detectives also raided the SNP’s headquarters close to the Scottish parliament in Edinburgh.

Sturgeon was also arrested as a suspect in June 2023, four months after unexpectedly quitting as party leader, but was later cleared of wrongdoing. The couple separated after Murrell’s arrest and announced their divorce last year.

Beattie, who was also arrested, was cleared by police and never charged.