Dr Michael Day worked as a GP in Dunstable, Bedfordshire
A GP and a six-year-old girl have become the latest to die after contracting the swine flu virus.
Dr Michael Day died on Saturday in Luton and Dunstable Hospital, but the NHS said the exact cause of death in the case is still unknown.
A swab test taken from Dr Day at the hospital has been confirmed as being positive for the H1N1 swine flu virus.
Chloe Buckley, six, from west London died after contracting swine flu on Thursday.
A patient in Essex who passed away earlier this month was the first person in the UK without underlying health problems to die of swine flu, but it is not yet clear whether these two latest cases suffered from any other type of health problem.
The NHS said the case of Dr Day, who was from Dunstable, has been reported to a coroner for investigation.
This latest death brings the total number of swine flu-related deaths in the UK to 17.
Dr Paul Hassan, senior partner at Priory Gardens health centre in Dunstable, where Dr Day worked, said: "This news has come as such a shock to us all and we are completely devastated.
"Dr Day was a work colleague and also a personal friend to everyone at the practice.
"I know the news will also come as a great shock to our patients, many of whom have known him for many years."
Dr Laurence Buckman, chairman of the British Medical Association's GPs Committee, said: "Doctors have always accepted that there are risks associated with their job. Obviously these are smaller than they used to be with the advent of modern medicine, but they can never be eliminated altogether.
"It is understandable that people will be worried when they hear that a GP has died but we urge them to follow the recommended advice and contact their family doctor, rather than physically going to the surgery if they have symptoms.
Chloe Buckley's school flew a flag at half mast in tribute to her
"We must remember that every year there are deaths from complications of seasonal flu - this is unfortunately inevitable with any strain of influenza."
Prof Steve Field, chair of council at the Royal College of General Practitioners said: "While the cause of Dr Day's death has yet to be confirmed, it is extremely important to remember that swine flu is currently a relatively mild condition in the majority of cases.
"The Royal College of General Practitioners has been working with the government on robust flu pandemic plans for a number of years and we are confident that the systems we have in place will cope well with the current pandemic."
England's chief medical officer Sir Liam Donaldson told the BBC that Dr Day's case was "very sad".
He added: "He was a very, very, dedicated doctor, loved by his patients and his colleagues, and it's a terrible tragedy that he should have died in this way.
"Anti-viral drugs are available to treat healthcare workers at the first sign of any symptoms, but ultimately they will be one of the priority groups whenever the vaccine arrives in the autumn."
'Bright and tenacious'
Meanwhile, tributes have been paid to Chloe, who attended St Catherine's School in West Drayton, west London and died at St Mary's Hospital in Paddington, London.
Head teacher Sara Benn said the news was "devastating": "It is impossible to put into words the sorrow that the whole school feels in such tragic circumstances.
"Chloe was a bright and tenacious student with a keen interest in sports.
"She will be missed by her fellow pupils and her teachers at the school."
Chris Spencer, director of education and children's services at Hillingdon Borough Council, confirmed that the school would be closed.
"This is a little girl who until a few days ago in all our minds was a child that was perfectly healthy so everybody here is in a deep state of shock and with just a few days to go until the end of term, we've decided it's in the best interests of all involved," he said.
Health Secretary Andy Burnham said the UK was among the "most prepared countries in the world" to deal with swine flu.
"We have been working closely with the Royal Colleges and staff bodies to protect and prepare frontline health workers, who are at the heart of our response to this outbreak, whilst providing the best health care possible to patients," he said.
Liberal Democrat health spokesman Norman Lamb said that NHS staff must have access to support and advice "given the anxiety that many of them may face".
He added: "The government needs to ensure that all frontline NHS staff are given access to flu vaccines as a matter of urgency.
"It is extremely worrying that GPs are still raising concern over the lack of clarity over who should now be receiving anti-viral treatment."