When Prince William talks, people listen - that's why he is so important to the mental health struggle

So Cinderella does get to go to the ball...

No, not the person of fiction, but the Cinderella issue of mental health, last night (10 October) the focus of a big reception at Buckingham Palace.

Walking up the wide, thick red-carpeted staircase, I thought of previous visits there. Most significantly perhaps, in May 1997, to an ante room with colleague Jonathan Powell as we waited with Palace courtiers for Tony Blair to emerge from his meeting where the Queen was asking him to become Prime Minister. Then a few years later, in the aftermath of Princess Diana's death, when I was seconded to help plan the funeral and found myself, oddly for a republican, in the position of advising the Royals on the navigation through what felt like very choppy anti-monarchist waters.

But as my partner Fiona and I arrived into the vast hall where the reception was being held, I remembered the last time I had been in that room, for the farewell party for one of the Queen's senior courtiers. As the Queen stood on a small dais and spoke warmly about the departing official, and we surveyed the massed ranks of establishment figures before her, lots of wavy white hair, pinkie rings, florid cheeks on the men, blueish hair and glittering pearls hanging from many of the women, barely a black face in sight apart from those serving the drinks and canapes, Jonathan leaned over and whispered 'I fear we have failed in our mission.'

Yet last night, on World Mental Health Day, with regards to another mission, it felt like we were winning. With Prince William standing where then his grandmother stood, on the issue of mental health it felt like the battle for parity between physical and mental health was being won, and that the young Royals were playing a big role in that battle.

Last night was very much for the people on the frontline of mental healthcare, people who have worked in mental health services when the stigma and taboo were at their height, when there weren't celebrity campaigns and big documentaries and storylines in soaps to help shift attitudes, when most politicians didn't even bother to pay lip service, let alone make it a priority.

Yes, there was a handful of the long-time campaigners like Stephen Fry, Ruby Wax, Marjorie Wallace (who founded Sane) and a tiny smattering of politicians who have taken a special interest like Nick Clegg and Andrew Mitchell. But the vast bulk, as I discovered from the dozens of little conversations as people buzzed around each other, were working for specific small organisations in specific areas, and making a difference where they could.

Understanding the monarchy

I have never fully understood the relationship between the monarchy and the people, but there was definitely an excitement in the room, and the feeling that people were being honoured for the work they do, even if there was no medal at the end of it. That excitement mounted when William, his wife Kate and his brother Harry entered the room and began to mingle. It may all be a bit weird, given they are just flesh and blood like the rest of us, but the impact was real.

William spoke about why they had all got involved in this: Katherine – as he calls her – because of her work with young women often crippled by anxiety, Harry because of his work with veterans often more injured in mind than body, himself having been a helicopter air ambulance pilot often picking up the pieces from suicide.

As earlier when he and Harry spoke at a reception down the road at St James's Palace to thank those who supported their Heads Together charity and the OkToSay series of films, the message was clear and simple – there should be no shame and much better understanding of mental health and mental illness, and bringing it out into the open is an important part of stripping down the shame and increasing the understanding.

Fiona and I made one of their films. We were surprised to be asked but pleased to take part, knowing as we do both from our journalistic and political days that Royal involvement can put booster rockets on any campaign they choose to adopt. The small number of films have now been viewed more than fifty million times. That is hopefully tens of millions of people being led to a different take on mental illness, what it is and what it is not.

GQ interview

I also interviewed William for GQ at the time and the reaction to that showed once more the remarkable reach they have. It got picked up and covered all over the world. Partly that was because he gives very few interviews and until then had talked very little about his mother's death 20 years ago. But it was also because of that global fascination in the leading characters in our Royal family.

As the St James's speeches ended we were all lined up in little groups and William came over to chat. Part of the reason I wanted to interview him was to see whether he was serious about the issue – he was – and also test whether he was likely to stay with it for the long term. I am pretty confident on that front too.

So we chatted, two lifelong republicans and and a future king. He said he was pleased the way the GQ interview came out, also thanked me for saying nice things about his mum in the documentaries about her death, said he had enjoyed 'introducing her to a new generation,' but also that he felt we really were making progress on the mental health front.

It was 'Katherine', he said, who first had the idea of the three of them working on this together. The whole point of Heads Together is, as Harry said, that two heads are better than one, three better than two, and so on.

They announced their future plans for the campaign, with a focus on veterans, but also digital support for youngsters challenged by mental ill health, and also that they were planning to take the campaign into schools.

William has definitely thought about all this deeply, and not just from a personal perspective given the struggles he has had with grief. He told us he felt that the problem with men feeling less able to talk about their mental health could be traced back to the First World War, when so many young men saw so many dreadful things, but the general cultural stance post war was 'not to talk about it.'

He said there is a place for the stiff upper lip, especially for someone like him with a formal role in the affairs of state. But generally the more we talk about our emotions, the better and happier we will be.

The Buck House reception was a remarkable, and very happy event. As the several hundred people who attended go back to the frontline of mental health care today, at least they do so knowing that the ugly sisters of stigma and taboo are finally being laid to rest, and the Cinderella service of mental health is getting the recognition, if not yet the funding, that it needs and deserves if we are to become a truly civilised and happy nation. The young Royals have definitely played their part in that.

Alastair Campbell is an ambassador for Time to Change, which this week celebrated its tenth anniversary, and a patron of the Maytree sanctuary for the suicidal