The singer-songwriter last month called a live phone-in segment on Sky News and offered to pay for people to have hospital scans, having just returned from having a scan himself.

Wearing a cream roll-neck jumper, knee-length coat, black trousers and dark blue trainers, he shook hands with a series of NHS staff outside a mobile MRI scanning unit and posed for photographs.

He joked “let’s all have a sing-song” and signed his autograph for a fan, before speaking to reporters.

Sir Rod’s donation is covering a day of scans for patients, which are being carried out at private healthcare firm InHealth’s mobile MRI scanning unit which is currently positioned at the hospital site.

Explaining how he came to pay for a day of scans at his local hospital, Sir Rod said: “I had just come from my scan in a private clinic near Harley Street.

“I walked in and said, ‘I’m terribly sorry I’m half hour late’.

“They said, ‘don’t worry, there’s hardly anybody in here today’.

“There were eight people with hardly anything to do.

“Then I thought this is a terrible injustice, so here we are.”

He said he was “here not to talk about politics, please, because otherwise it overshadows what we’re trying to do”.

Sir Rod, who has had six number one hits in the UK charts, said he would like to pay for scans elsewhere too.

“If this is a big success, which I think it will be, I’d like to do it in Belfast, Dublin, Edinburgh, Glasgow, Manchester, and just keep it going, and hope some other people follow me,” he said.

“Because I want to prove I’m not all mouth and trousers and that’s why I’m here to prove that I followed through with it, ok folks.”

He added: “There must be enough money in the coffers to pay up for these nurses – only two years ago we were clapping and now…

“Bless them, they work so hard, salt of the earth.”

Pressed on the state of the NHS, the pop star said: “We’ve got to sort this out, really.

“We’re in dire straits.

“If I am going to get political, I think we should send the Ukrainians F-16s.

“It’s up to you, Prime Minister.

“I’ve been supporting them for years, Ukrainians.

“On stage I have the flag and I wear a blue and yellow suit and do a song and dedicate it to them.

“I feel very strongly about it.

“If the Ukrainians lose it’s the end of civilisation as we know it, it’s all over.”

After speaking to reporters, Sir Rod climbed the steps to the mobile MRI scanning unit – which was positioned outside the hospital – and waited behind the exit door to surprise a patient.

As patient Omarie Ryan went to leave the unit, the Forever Young singer said “behind the door” and moved his hand into sight for a handshake.

Sir Rod then posed for selfies with 36-year-old Mr Ryan, who had travelled from London for a routine left knee scan.

The star said: “So this is my first customer!

“All good pal? You take care of yourself, stay healthy, alright mate.”

To laughter from the gathered crowd, he added: “And I have a new CD coming out in five weeks!”

Mr Ryan said afterwards: “It was a dream come true.”

Stephanie Lawton, chief operating officer at the Princess Alexandra Hospital, said Sir Rod paid for a day of scans at the hospital which would help reduce their waiting list by around 10%, or around 20 patients.

“Rod’s a local resident, we’re his local hospital, we’re really delighted to be working with him and his team for the benefit of patients and doing everything we can to reduce the waiting lists,” she said.

Ms Lawton added: “It would be fantastic if he would continue to work with us.

“We’ve got a charity, he would be a massive supporter for the organisation. We would be delighted if he wanted to continue the links.”