Prince William and Boris Johnson attend NHS service of thanksgiving at St Paul's Cathedral

The Duke of Cambridge and Boris Johnson joined health chiefs at St Paul’s Cathedral this morning for a service honouring the 73rd birthday of the NHS.

The Duchess of Cambridge, who had been due to attend, was forced to pull out after coming into contact with someone who tested positive for coronavirus and is now in isolation.

Prince William will later host an NHS Big Tea at Buckingham Palace alone.

NHS chief executive Sir Simon Stevens addressed the congregation at St Paul's, describing the occasion as an opportunity for "cautious pride in science, treatments and our vaccines" but also a time for some "anger and regret" over the millions who have died with coronavirus around the world.

He described the NHS as an example of "building back better" and "an inspiring example for our generation of how out of adversity can come strength".

Sir Simon addressed socially-distanced guests including frontline NHS workers, Labour leader Sir Keir Starmer and Liberal Democrat leader Sir Ed Davey.

Ahead of the service, the party leaders spoke for a few minutes before taking their seats at the front of the cathedral.

Also present at the event were Jonathan Van-Tam, the deputy chief medical officer for England, and Professor Stephen Powis, NHS England national medical director, who were seated ahead of rows of socially-distanced frontline NHS staff, volunteers and carers.

The service celebrated their contribution to the country during the pandemic.

Dr Ashley Price, who treated the first coronavirus patients in the UK, welcomed the final lifting of restrictions due on July 19 - but said he believed masks will still be needed in some settings, including hospitals.

He said: "The news is looking good.

"We're having fewer admissions to hospital and those that are coming in we're generally able to treat.

"We do have to remember though that there are a lot of vulnerable people in our society - people for whom the vaccine may not have worked as well - and we need to be mindful of that.

"I think, in places like hospitals, mask-wearing will need to continue for a bit longer because we are still contracting coronavirus and it's possible to spread it to very vulnerable patients."

The choir sang the national anthem at the close of the hour-long ceremony, before the Duke followed a procession of religious leaders past rows of frontline healthcare workers to the exit.

The Prime Minister filed out shortly afterwards.