Almost half of British men and 4 in 10 women could be obese within 20 years, according to a study published in the Lancet Journal.
Researchers warn that a total of 26 million Britons will be clinically obese by the year 2030.
With the NHS expected to cut Ģ20 billion over the next four years from its budget, patients without private health insurance are likely to suffer the consequences of an obese Britain.
Currently, the NHS is spending 8 per cent of its medicines bill, treating diabetes caused by obesity.
But by 2030, almost half a million more people could suffer heart disease, with nearly 700,000 extra cases of diabetes and 130,000 more suffering from cancer.
These rising figures are estimated to cost the NHS an extra Ģ2 billion a year.
Public Health Minister Anne Milton said the government believed the best way to reduce obesity was through a "collective voluntary effort".
She said: "We have no current plans to impose a 'fat tax', but we are working with food companies to reduce fat, sugar and salt and ensure healthier options are available."
But sceptics say that in a society that relies on junk food, television, and the Internet, more drastic measures are needed to relieve the pressure on the NHS.
At present, the number of people waiting for NHS care has gone up by 61 per cent per year, and projections show that this is likely to continue.
If the Lancet's predictions prove to be true, the private health sector will likely boom. People who have private health insurance will be able to bypass lengthy NHS queues and avoid the effects of the obesity crisis.