A "perfectly healthy" six-year-old girl died of swine flu within hours of being taken to hospital after complaining of a sore throat, it has emerged.
Chloe Buckley, from north west London, died on Thursday a day after her GP wrongly diagnosed her illness.
Sky reporter Victoria Gatenby said: "Chloe's parents took her to their GP on Wednesday with a sore throat.
"The GP diagnosed her with tonsillitis, sending her home without Tamiflu, which is the drug that combats swine flu."
The youngster's condition quickly deteriorated and she was taken to the accident and emergency unit at Hillingdon Hospital in Uxbridge.
On Thursday she was transferred to St Mary's Hospital in Paddington, but despite doctors' efforts she died.
Chris Spencer, director of education and children's services for Hillingdon Council, said: "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."
The Government's Chief Medical Officer Sir Liam Donaldson said investigations are continuing into whether or not Chloe had underlying health problems.
Chloe was a pupil at St Catherine's School in West Drayton, north west London.
Headteacher Sara Benn said: "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. Our thoughts are with her parents and family at this time."
Hillingdon Council has temporarily closed the school because of the "exceptional set of circumstances".
Bedfordshire GP Dr Michael Day is also among the latest UK swine flu victims - taking the number of British deaths to 17.
Dr Day died on Saturday in the Luton and Dunstable Hospital.
A swab test taken at the hospital confirmed him as being positive for the H1N1 Swine Flu virus.
The exact cause of death in this case is still unknown.
Dr Paul Hassan, senior partner at Priory Gardens Health Centre, said: "This news has come as such a shock to us all and we are completely devastated."
The latest deaths come after the first British patient without underlying health problems died on Friday after contracting swine flu.
The patient, from Essex, died in Basildon.
Nearly 10,000 Britons have been confirmed with swine flu after it spread to the UK from Mexico.
However, hundreds of thousands more people in the UK are thought to have the virus.
The total number of cases in the country are now being estimated rather than counted individually.
The UK has the third highest case total in the world after Mexico, which has 10,262 cases, and the US, which has at least 33,902.
Sir Liam told Sky News he expects the virus will "move quickly" in the autumn and winter.
"The number of people treated will put pressure on the NHS but for those of us who are dealing with it, we will not be alarmed by the spread of the pandemic," he said.
The Government has ordered enough swine flu vaccine to cover the entire population, with the first doses arriving next month and half of all doses expected by the end of the year.
A list has been drawn up of people who will gain first access to Tamiflu, including health workers and patients with conditions like diabetes and asthma.
:: The NHS advises anyone who thinks they might have flu to check their symptoms on
www.nhs.uk or call the swine flu information line on 0800 1 513 513.
