The Duke of York is a “dead man walking” who has to “fall on his sword” for the sake of the monarchy and strike a deal with his accuser Virginia Giuffre, a lawyer has said.

Mark Stephens said Wednesday’s ruling that Andrew is to face a civil sexual assault trial has “thrown a bomb” into the heart of the royal family and threatens to spark a constitutional crisis.

US Judge Lewis A Kaplan has decided the Queen’s second son can be tried over allegations he sexually assaulted Ms Giuffre when she was 17.

Speaking to the BBC, media lawyer Mr Stephens said a crisis of this scale was unprecedented for the royal family.

“Prince Andrew has nowhere to go. He’s effectively a dead man walking as far as the royal family is concerned,” he said.

“But the one thing he can do is to accept the responsibility, accept the blame, accept that he has to fall on his sword for the sake of the wider royal family.”

The duke has vehemently denied the allegations.

Mr Stephens added: “This is the first time that Prince Andrew’s problems have reached into and are beginning to touch the wider royal family.

“There will be crisis meetings taking place. Downing Street will be being consulted. The Privy Counsellors will be called in and of course, the most central advisers to the key members of the royal family will be coming in to deal with this crisis, a crisis that they have never seen before.”

He suggested the duke could appeal against the ruling, but put his chances of success at 40%, and said his best option was to try to settle the case with a financial payment.

“Whether he denies it or not, he’s going to have to buy this case off as a matter of realpolitik,” he said.

He added: “We are really, with Prince Andrew, in the last chance saloon with the towels over the taps.

“The only thing that makes this worse is that Prince Andrew has to start giving evidence in this case, whether that’s about his sweating, or his trip to Pizza Express or worse still, he has to deal with the allegations of what he is supposed to have done with a 17-year-old woman.”

Judge Kaplan’s decision is a huge blow for Andrew, whose lawyer argued the case should be thrown out as Ms Giuffre had waived her right to pursue the duke by signing a confidential settlement with disgraced paedophile financier Jeffrey Epstein.

Mr Stephens said: “Judge Lewis Kaplan has thrown a reasoned judicial decision like a bomb into the middle and the heart of the royal family and threatens to provoke constitutional crisis as a consequence.”

He suggested Ms Giuffre has “many of the cards” in this case if Andrew has to settle at all costs, meaning the price of a financial deal would go up.