The website Flusurvey.org allows patients to report symptoms and compiles the data to predict an approaching surge in consultations.
Developers believe the tool is particularly useful as many people with flu symptoms do not visit their local practice.
Traditional flu surveillance methods rely on information that is generated by consultations at practices.
Anyone in the UK can register to provide weekly updates on flu-like symptoms and previous years have attracted 5,000 volunteers. The data is also sent to the UK’s Health Protection Agency.
Professor John Edmunds and colleagues at the London School of Hygiene and Tropical Medicine developed the tool.
He said: ‘Being able to detect a flu epidemic before hospitals and GPs are snowed under with patients is vital.’
Meanwhile, leaders from health unions and the medical colleges have again urged NHS staff to get vaccinated against seasonal flu. Just 34.7% received the vaccine last winter.
A statement from NHS Employers said: ‘It’s vital that staff protect themselves, their families and those in their care. We want having the vaccine to become routine and to be seen to be as important and fundamental as good hand hygiene in protecting the most vulnerable in our care. This simple act could save lives, including health workers and their families.’