The prime minister has joined a nationwide applause to pay tribute to NHS staff on the 72nd anniversary of the health service.
The round of clapping was inspired by the weekly Clap for Carers initiative to thank key workers during the height of the coronavirus pandemic.
Boris Johnson said he celebrated with staff who "quite simply, saved my life" after he caught the virus.
It is hoped the anniversary applause will become an annual tradition.
Speaking after applauding outside Downing Street, Boris Johnson tweeted: "Thank you to the whole NHS family and all of our carers for all you have done and continue to do to keep us well and cared for.
"In these past few months, indeed the past 72 years, you have represented the very best of this country. Our gratitude to you will be eternal."
He later added in a statement that he had marked the occasion with staff from St Thomas' Hospital, who cared for him when he was admitted to hospital with coronavirus in April.
A World War Two Spitfire plane with the words "Thank U NHS" painted on its underside tipped its wings above hospitals and the homes of fundraisers and volunteers, recognising the way people have supported the NHS and local communities during the pandemic.
Labour leader Sir Keir Starmer said the celebrations were "very personal for me" as his late mother was a nurse and later relied on the health service when she became ill.
He said: "Many, many times she got gravely ill and it was the NHS that she turned to, and I remember as a boy, a teenager, being in high dependency units, in intensive care units, with my mum, watching nurses and other support staff keep my mum alive.
"They did that on more than one occasion - it's etched in my memory. For them, it was just the day job. They were doing that every day."
The National Health Service was launched on 5 July 1948, with the core principle that it is free at the point of delivery and is based on clinical need.
As part of a weekend of anniversary events, UK landmarks were lit up blue in celebration and remembrance on Saturday.
Downing Street, the Royal Albert Hall, Blackpool Tower, the Shard and the Wembley Arch were all illuminated and a minute's silence was held to remember those who have died during the pandemic.
The latest government figures, released on Sunday, showed a further 22 people had died in the UK after testing positive for coronavirus, bringing the death toll to 44,220.
People were also asked to place lights in their windows in a show of remembrance on Saturday night, with the Archbishop of Canterbury, the Most Reverend Justin Welby, lighting a candle in Canterbury Cathedral.
First Minister of Scotland Nicola Sturgeon was among officials joining in with the nationwide applause on Sunday evening.
In a video message she said the country was "depending more than ever" on its health and care workers, and thanked them "from the bottom of my heart".
First Minister of Wales, Mark Drakeford, said NHS staff and social care workers were "all heroes".
And Captain Tom Moore - who raised more than £32m for the health service by walking laps of his garden during lockdown - shared a video of himself clapping from his armchair at home in Bedfordshire.
The idea for Sunday's round of applause was inspired by the success of the weekly Clap for Carers, which saw households across the country show their appreciation for the NHS and other key workers during the lockdown.
Annemarie Plas, who founded the Clap for Carers initiative, joined Prime Minister Boris Johnson outside No 10 for the clap at 17:00 BST.
Speaking on BBC Breakfast on Sunday morning, she said: "We have had this first part of the crisis, we don't know what lies ahead, so if we can have this one moment where we say thank you to each other and recharge our batteries for what may be a heavier time that lies ahead, then I think that is a beautiful moment."
She said the NHS helped her when she arrived in the UK from the Netherlands as a new mother, "so I feel very happy to be in touch with the NHS this way".
Ms Plas added that the celebrations were "not just about the NHS" but about others who have also "sacrificed so much" during the pandemic - such as "delivery workers, teachers, parents, good neighbours".
The Duke and Duchess of Cambridge praised healthcare workers on a visit to Queen Elizabeth Hospital in King's Lynn, Norfolk.
The couple chatted to staff and volunteers about how they coped during the first wave of the epidemic.
The Prince of Wales paid tribute to staff working through "the most testing time in the service's history".
In a video message to mark the occasion, Prince Charles spoke of his gratitude and pride for the "costly sacrifices" of NHS staff.
"Despite all that has been endured, there is deep cause for gratitude, and a true reason for pride," he said.
The prince also said the pandemic had brought out the best in people, adding: "This renewal of our community spirit has been a silver lining during this dark time."
Speaking at a rally celebrating seven decades of the health service, Labour leader Sir Keir said NHS staff needed a pay rise in the wake of the pandemic.
"It's very important that we don't just say thanks, but recognise in a meaningful way what the NHS has done," he said.
His comments come after unions representing more than 1.3 million nurses, cleaners, physiotherapists, healthcare assistants, dieticians, radiographers, porters, midwives, paramedics and other NHS employees wrote to the chancellor and the prime minister calling for pay talks to start soon.
Meanwhile, about 100 protesters gathered at Marble Arch in London, calling for the end of racial disparity in the health system.
One of the organisers, Tyrek Morris, 21, told the crowd: "We are protesting for black lives and one of the demands we have is to abolish the racial disparity within the NHS, especially towards black women.
"We need to implement extensive measures to prevent the disproportionate suffering of black women in healthcare and bring to an end the significantly increased black maternal mortality rate."
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