A former royal protection officer has issued one of the starkest warnings yet over the Andrew Mountbatten-Windsor scandal - claiming Prince William may ultimately have to be questioned if the monarchy is to survive. Speaking on TalkTV, ex-royal bodyguard Dai Davies told host Jeremy Kyle that the spotlight now falling on palace insiders was not only justified, but long overdue. Asked whether it was unfair that former royal protection officers were being scrutinised, Dai replied bluntly: "No, sadly I think it's reasonable - and that's the best word in the English language."

He explained that officers who travelled with Andrew for years would have been exposed to far more than has ever been publicly admitted. "If they went around the world with him for all those years, stayed in those five or six different premises from Paris to the Virgin Islands and so on, they must have seen something," he said. "So they are crucial if you're going to have a proper police inquiry." Dai added that he had been calling for a full investigation "for a number of years", saying protection officers were "with him close as anyone".

He also questioned how basic checks appeared to have been missed before Andrew's most controversial trips.

Dai continued: "The big question that has to be asked, which I can't understand why nobody did due diligence before they went, particularly on that nine-day stay. Didn't the embassy warn anybody? Or the High Commission?"

The former officer said protection teams would have carried out reconnaissance on properties Andrew stayed in - including those linked to Jeffrey Epstein.

"I think the record shows that at least two of them stayed there," he said. "They would have done a reconnaissance. They would have gone there. They should have checked out who Mandelson was."

He claimed it would have been impossible not to notice disturbing signs. "You couldn't possibly not see the lewd pictures on the walls," Dai said when discussing Epstein's home. "There were sexual objects in virtually every room, it is alleged."

As the discussion turned to whether the scandal could reach the very top of the monarchy, Dai did not hesitate.

"If any royals knew of this, then unfortunately, they have to be questioned too," he said. Jeremy asked directly whether that could include Prince William.

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"I think they have to be, don't they?" Dai replied. "If they were party to any kind of issue which Andrew has stated."

From an investigator's perspective, he said, the public had been treated with contempt.

"Don't take us for fools," he said. "Don't take the Michael that we will buy some of this nonsense that's been emanating for years."

Dai repeatedly returned to what he described as a long-running "conspiracy of silence", claiming the palace had known about serious concerns since at least 2011.

"They knew perfectly well back in 2011," he said. "They monitor everything that goes on." "For 14 or 15 years there has been a conspiracy of silence - by many at various levels - not to tell the truth."

He also questioned why Andrew was stripped of his titles if there was supposedly nothing to answer for. "You wouldn't take every title, everything the man has had all his life, unless you were pretty convinced he was guilty," Dai said.

"It just beggars belief. For the monarchy to survive, we need transparency," he said. "Be honest. Tell the truth."