INGRID SEWARD: Prince Philip will turn in his grave after Harry ignored his wishes and effectively abandoned his surname

There are certainly good reasons for Harry and Meghan to adopt ‘Sussex’ as their surname.

Perhaps, as Meghan has suggested, it will “unify” her family, although I’m not sure how. ‘Unify’ is not a word I associate much with Montecito.

Maybe keep things clean and simple in brand-conscious America, where the subtleties of aristocratic titles are little known or understood.

But in the world of British royalty – where dukedoms have their origin – everything is a little different. There are rules for those who inherit these privileges or are granted them.

(The title Duke of Sussex was a gift from the prince’s grandmother, Queen Elizabeth, on Harry’s wedding day in 2018.)

And I fear that this is a move that will only serve to further distance the prince and his children from the Royal Family, from their British roots and from a father and grandfather, the King, now diagnosed with cancer.

A distinction must be made here. Not everyone is opposed to Harry using Sussex as a surname.

After all, that kind of thing has a history. Consider, for example, Princess Margaret’s husband, who was granted the title Earl of Snowdon after marrying the Queen’s sister.

He legitimately used the name Tony Snowdon, both socially and professionally.

As the wife of a royal duke, it is perfectly acceptable for Meghan to be called Meghan Sussex. Why not?

But it’s different for the children, Archie, four, and Lilibet, two.

His surname is Mountbatten Windsor, and should remain that way. ‘Sussex’ is not correct. It’s not even a surname.

Few Americans will feel very concerned about any of this, and it’s hard to avoid the suspicion that the United States is the only place that registers with Meghan.

However, the royal family does care about these things and so does the British public.

Furthermore, the surname Mountbatten-Windsor has a particular meaning.

Philip was dismayed to discover that when his wife, Princess Elizabeth, became queen in 1952, his children (and his children’s children) would not bear his surname, Mountbatten.

Rather, they would be the Windsors, named after the Queen’s family.

Felipe was furious and hurt. The decision was considered emasculating and cruel.

“I am the only man in the country who is not allowed to give his name to his children,” he protested.

“It hurts him,” Countess Mountbatten, wife of Philip’s uncle and mentor, Lord Mountbatten of Burma, recalled at the time.

‘He had given up everything for his wife and how this, the final insult. “It was a terrible blow.”

It was the elder statesman Winston Churchill who found a solution, encouraged by the young queen’s private secretary, Tommy Lascelles, a savant some 40 years her senior.

Together, Churchill and Lascelles forced Elizabeth (she lacked the confidence to do it alone) and it was agreed that all male-line descendants of the royal couple would be called Mountbatten-Windsor, apart from those who were princes and princesses.

A discreet commitment.

How sad, therefore, that just three generations later, Harry would so blatantly ignore his grandfather’s wishes and effectively abandon the family name that Philip had fought for.

Harry professed to respect and love the Duke of Edinburgh and I’m sure he did and always will, but this latest debacle would make Philip turn in his grave.

Do Harry and Meghan think they’re being smart? Perhaps this is an attempt to entrench the Sussex name so firmly that, whatever the political atmosphere in Britain, the title can never be effectively removed.

Perhaps they are simply ill-advised.

But it’s hard to avoid the suspicion, as it has been from the beginning, that the Duke and Duchess of Sussex want to have it all.

Be real, but with the style you choose. Having the status while maintaining the freedom to choose the obligations that go with that status.

Changing his last name can only be a provocation for Harry’s father at a time when he has more pressing things to think about.

Of course, there is little the King can do without appearing rude. He will feel that he has no choice but to turn the other cheek, as he has done for a long time, even if tolerance often comes at a considerable mental cost.

The saddest thing of all is that I am sure Prince Harry still loves his family and, in his heart, hopes for a reconciliation.

However, once again, it is driving them away.

• Ingrid Seward is the author of My Mother & I: The Relationship Between Charles and the Late Queen, published by Simon & Schuster.