When Princess Diana announced that she was stepping back from public life on December 3, 1993, during a speech at the brain injury charity Headway, her loyal bodyguard Ken Wharfe was not at her side.

Just weeks earlier, the Royal Protection Officer had sparked a flurry of newspaper headlines after stepping back from being Diana’s bodyguard for more than six years.

Now, Wharfe, 77, has revealed that he felt unable to keep the Princess safe after her separation from Prince Charles, the previous year. And he has claimed that her decision to abandon her security officers ultimately led to her death.

Speaking about her death in a new Channel 5 documentary Diana: The Princess and the Bodyguard, he said: ‘I reflected back to that moment when Diana abandoned her security because I knew deep in my heart that without it, she would ultimately perish.’

From the moment that Wharfe joined the Royal Household in 1986, to look after Princes William and Harry, then four and two respectively, he had a front-row seat to the Wales’s disintegrating relationship.

Within a year, he was working as the Princess’s bodyguard – her previous protection officer Graham Smith had been diagnosed with terminal cancer and Diana appointed him to the ‘A team’.

However, on December 9, 1992, after the publication of the Andrew Morton book Diana: Her True Story, Buckingham Palace announced that the couple was separating.

‘It wasn't until I went back to Kensington Palace a few days later that she said: "Did you hear the news, Ken?" And I said: "Yes." I said: "How are you feeling?" "Well, it's over."

‘She was incredibly tearful because let’s not forget when a statement like that is made to the world that your marriage is effectively over, that's a very distressing thing to hear. But clearly in my view, this is what she wanted. She wanted out of this marriage.’

Over the next year, her relationship with her bodyguard became increasingly fractious. ‘1993 became a very, very difficult period for Diana,’ added Wharfe. ‘You know, she was actually thinking about what do I do next?

‘When do I get divorced? What do I do when I'm divorced? She had spoken many, many times before about normality and I think she was looking for greater freedom.’

That March, Wharfe accompanied Diana to one of her favourite skiing resorts in Lech, Austria, but the princess was already pushing boundaries.

‘It was early one morning about half past six, I was awoken by my night security officer who said to me rather sheepishly, that Diana had just come into the hotel, come back to the hotel.

'"What do you mean, just come in? Are you telling me that you let her out?" And he said: "No Sir, I didn't." "So how did she get out then?" He says: "I don't know." He couldn't really work out, how she'd actually left the hotel.

‘So, I went outside to the front of her suite and the balcony that she had. There had been a heavy snowfall that night - I mean, I was now treading in it with up to my waist.

‘But I could see this almost human like impression in this deep snow and then these steps away from the balcony. Much to my utter amazement, I realised she must have jumped about 20ft down from this first floor balcony.

‘She could have died. I mean, making no small point about it. I was actually concerned, really, for her own mentality. Quite what was her state of mind in actually attempting or believing that she could do something like that.

‘I had to establish that Diana was safe, that she was in the hotel. So, I then went and knocked on her door. And she was very, very happy, very buoyant.

'"Oh, hello, Ken, come in." I said: "Yes, are you okay?" And she said: "Yes. I just needed a bit of air, Ken." So, I said: "That's a pretty stupid thing to jump from that balcony."

‘She said: "I just decided I wanted out. I didn't want to disturb your colleagues. I didn't want to make a fuss about it." I said: "It could have been a real fuss had you killed yourself."'

The turning point came in 1993 when Diana was driving back to Kensington Palace, with Wharfe in the front passenger seat.

‘She said to me: "Oh, I need to do some shopping in Kensington High Street. You can park the car." And I said: "I'm not parking here there are yellow lines here. We can't."

"Well, you can deal with that, you're a police officer." I said: "Ma'am, what's the matter with you? You know that I can't do that." "No, I want to do some shopping." "Okay. Then we do it together and we park the car sensibly."

‘And she became rather agitated about it. There was a slight urgh, as if to say: "Oh, okay. Alright then." At which point Diana's door opened and she ran to Kensington High Street…

‘Luckily, I knew where she was going, so I walked down to Tower Records. I waited there for ten or 15 minutes, and Diana eventually came out. Afterwards, we drove to Kensington Palace, we arrived at the front door and she went inside.

‘I felt this isn’t really how security should be conducted with your charge effectively running away from the protector. I went home that evening and thought have I reached a point now where I can no longer honestly guarantee her safety and security.

‘The following day, we carried on the day's duty, and we arrived back at Kensington Palace in the late afternoon and I remember saying to her: "Before you go, ma'am, may I have a quick word with you?" And she said, "yes, of course."

‘I said: "Look, following on what happened yesterday I'm afraid it’s not something that I'm prepared to accept. Because that really, for me, actually puts your safety in jeopardy and for that reason, I shall be leaving your service."

‘I think she was somewhat shocked, if I'm honest. I honestly don't think that she expected me to say that. I think she thought, well, we'll just carry on as we have done, but I could see things getting worse. And I wasn't prepared to run with that.

‘It was a difficult decision. I felt sad because I enjoyed the work that I did with her, but I felt it was the right decision, if only to guarantee her security. And I did not want to be part of a security team that failed her.’

Tragically weeks later, Diana abandoned her security team. ‘I thought it was a fatal mistake,’ he said. ‘Almost overnight Diana was without a protection officer.’

Wharfe found out that Diana had died in the early hours of August 31, 1997. ‘My pager was vibrating on the floor and I couldn't, for the life of me think, who would want to speak to me at this time of the morning.

‘It asked me to call head of royalty protection, New Scotland Yard. But I had no phone in the house. I was renovating this property. So, I walked to the public telephone box in the village.

‘I dialled the number and the boss answered and he said: "I've got some sad news for you. The Princess of Wales, Diana, has died in a car crash in Paris." And I was completely stunned by this.

‘Since the accident in Paris, I've analysed many, many times the security failures that occurred that night, of which there were many.

The failure of the protection team was very difficult for me to accept…

‘She tragically died when really should not have done. Had Philip Dorneau, the original driver, driven from the front of the hotel with a police escort and the paparazzi being given a photograph prior to that departure, Diana would not have died that night.’

Diana: The Princess and the Bodyguard airs on Channel 5 at 8pm on Saturday (December 27).