Experts believed two doses would be necessary, leaving practices facing a huge burden on top of the seasonal flu campaign.

But if the trial results prove conclusive, many patients may be able to make a single visit to their practice for vaccination against seasonal and swine flu, slashing the likely workload.

The trial, run by the University of Leicester and Leicester Hospitals, involved 100 healthy 18-50-year-olds.

Dr Ian Stephenson, who led the trial, said: ‘Results shows that the serum antibody responses were highest among subjects who received two doses of vaccine, however a single vaccine dose also induced responses associated with protection against influenza.

‘The results suggest that one vaccine dose may be sufficient to protect against the (A) H1N1 swine flu, rather than two.'