When I discovered almost nine months ago the jaw-dropping name and details of the Establishment 'plot' to return Prince Harry and Meghan to Britain and undermine the Prince and Princess of Wales, I couldn't believe the gall of the California-based couple.

The plot was known as 'Project Thaw' because its aim was to 'warm up' the Duke and Duchess of Sussex's frosty relationships with the rest of the Royal Family and with the British people. They had been in the deep freeze since the couple quit public duties to seek their fortune in North America and attacked the Royal Family in their bombshell interview with Oprah Winfrey, as well as in Harry's tawdry memoirs Spare and their Netflix 'reality show' Harry & Meghan.

When the couple arrive in Britain in less than a fortnight's time, accompanied by their children, Prince Archie, aged seven, and Princess Lilibet, five, it may appear that Project Thaw has been successful.

After all, it will be the first time that Meghan has stayed here since Queen Elizabeth II's funeral in September 2022 and even longer since their children were here in June of that year for the late monarch's Platinum Jubilee celebrations.

Not only that, but the family have been offered accommodation next month at a royal residence and King Charles is expected to meet them, just as he did for tea at Clarence House when Harry last came here for a string of engagements in September 2025. That was the first face-to-face meeting between father and son in 19 months.

The reason Harry and Meghan needed the help of Establishment figures in government and at the Palace was because they had lost their automatic right to taxpayer-funded security after they moved overseas.

This infuriated Harry, who took legal action against the Home Office, which he lost. After he also lost a legal challenge over the decision in May last year, he rushed to give a BBC interview in which he admitted to being 'devastated' and declared, emotionally: 'I can't see a world in which I would bring my wife and children back to the UK at this point.'

He has, however, apparently been satisfied by the security arrangements for next month's visit.

But while all these developments might suggest success for Project Thaw, there are two important ways in which it has failed to achieve its aims.

Firstly, while the King will, no doubt, want to see his grandchildren (in Lily's case, for only the second time in her life), there is no change in the icy relations between Harry and his brother, Prince William, I hear.

'It's a subject that's not even discussed anymore,' a friend of William and Catherine told me. 'He made clear some time ago that he didn't want anything to do with his brother, and that hasn't changed, as far as I know.'

The friend added: 'I doubt anyone knows what his views are on his father seeing Harry and Meghan, because he doesn't talk about it.'

Just like the King's dealings with his disgraced brother, Andrew Mountbatten-Windsor, William is happy to leave the 'Harry problem' to his father.

The second way in which Project Thaw has failed, so far at least, is in its aim of 'warming up' the Sussexes' relationship with the British people. I detect no more enthusiasm for the couple than there was last October. And that's hardly a surprise when they have failed to apologise for their insults to the rest of the Royal Family.

When I revealed the existence of Project Thaw back in October, a friend of the Sussexes told me: 'Meghan will return to Britain before the year is out.' The friend added, jokingly, that she would be 'bearing humble pie'.

In the event, it has taken longer for the former actress to return. And if she does bear that humble pie – and eat it – will her performance be enough to win her a second act with the British people?

Personally, I doubt it.