Surveying the new cancer care centre on the Ninewells Hospital site, designed by his friend the world-renowned architect Frank Gehry, Sir Bob was blunt, as chairman of the Maggie’s Centre Dundee Ian Wilson pointed out a design feature of the building where every beam is a different size and nothing fits together precisely, Sir Bob remarked, “They ****** up. That beam’s too short and are trying to tell us it’s art.”

But it’s all a front. This former pop idol turned global campaigner is a cultured man with an enormous appreciation of art in all its forms and a deep well of compassion for his fellow man.

A prolific swearer, nevertheless he is an eloquent speaker who brought a pack of Press hounds to a hushed reverence just by quietly starting to talk about his friend Gehry, “A dumpling of a man”, his love of his architecture and the “epidemic” that is cancer.

Of the quirky, domestic-scale centre with stunning views across the River Tay, Sir Bob said it was “an instant landmark”.

Looking towards the Ninewells Hospital building, Sir Bob said it was “a functioning machine” that existed to keep people alive.

“Then you come down here and this is to explain to you why life is worth living. That is what the building does. It is full of beauty on one of the most beautiful sites”.

He said the architecture did not dominate but was the kind of place that if he or any of his family would like to go if they had to face a diagnosis of cancer.

He said cancer was such an epidemic that he expected that, like the flu, he would get it at some stage.

He spoke movingly about the loss of his friend and road manager of 27 years, who died from cancer last year.

And he went on to say that such a place as Maggie’s Dundee would help people facing the disease as well as allowing them to appreciate wonderful architecture.

“Art is nothing more than humanity in excelsus”, he said.

Earlier, a tiny man, grey from head to toe, with shabby old grey jeans, a grey T-shirt and steely grey hair, stood self-consciously on a stairwell and began speaking about the building he designed at long distance in America.

Frank Gehry spoke movingly about his friendship with Maggie Keswick Jencks, the woman who died of cancer in 1996 and was the inspiration for the building.

He said she was, “a woman of means” but could not find anywhere the caring and supportive environment outwith the highly medicalised treatment areas of a hospital to meet her emotional and other needs when dealing with her diagnosis of cancer.

Disarmingly, he said he didn’t think Maggie would approve of his building, explaining that while they were very great friends, they had very different ideas about aesthetics and her taste was different from his own. “So had she lived she probably would not have hired me to do this,” he said.

But Gehry really wanted to deliver a building that would be worthy of his great friend and her aim to help other cancer patients.

To do that he said he specifically tried to capture a domestic feel within his building that would encourage people to feel comfortable and relaxed.

He was certain he did not want to create a “polemical statement” in architecture.

Very specifically he did not want people facing cancer to come across to his building and say, “I won’t go into this guy’s ego trip. I’ll pass on that one”.

Mindful of keeping his building on a small scale and non-intimidating, he nevertheless spoke of his desire to make it “the best thing” he had ever done, something that would be “the right thing for the right place, something Maggie would have been proud of”.

He explained his building, inspired by a Vermeer, was designed to be seen from above and that was why there was such enormous emphasis on the roof with its stainless steel tiles mirroring passing clouds and reflecting sunshine.

He said people would come down from the hospital and look upon the building from above before coming through the door.

Having designed the building from afar, he jokingly said, “I walked in and looked at it and said to myself I didn’t realise I was this good.

“I hope it works for other people.”

Also at today’s official opening of the new centre was Maggie Jencks architect critic husband Charles.

Clearly thrilled with the building, he said it was a church but not a church, an art gallery but not an art gallery and it would be different things to different people, but primarily it would help people suffering from life-threatening disease.

“Hospitals are factories for curing people, like machines, and they need to be supplemented by some kind of architectural space that lifts people and gives people the will to fight. I think this building is going to do that.”