Sir Liam Donaldson, the Chief Medical Officer, estimated that 19,000 people would die from the virus under the "worst case scenario", a significant drop from the figure of 65,000 given in July.
He said the revised estimations, calculated by Government scientists, were "assumptions and not predictions".
They are based on one in three people across Britain becoming infected, and do not take into account what impact the swine flu vaccine, due next month, will have.
Swine flu infected at least 100,000 Britons last week, officials announced on Thursday.
Sir Liam Donaldson, the Chief Medical Officer, said there were now 840 patients in hospital in England with swine flu, 63 of them in intensive care.
Children are being hit hardest, with relatively few cases amongst the elderly, as it is thought they may have some immunity to the H1N1 virus from previous pandemics.
more info from Telegraph
Speaking this morning, Andy Burnham, the Health Secretary, and Sir Liam Donaldson, the Chief Medical Officer, said that there were hotspots where swabbing and lab confirmations of the virus now put an unjustifiable strain on time and resources. These areas, including the West Midlands and London, are now shifting from the containment phase, which is led by the Health Protection Agency, to outbreak management, led by the strategic health authorities and local health trusts.