People could be putting their lives at risk by believing the flu is just a severe cold, the Government's head of immunisations has warned.

Professor David Salisbury, director of immunisation for the Department of Health, urged those in at-risk groups to visit their GP for the annual flu vaccination.

Everyone aged over 65 is eligible for a free jab but people with serious heart and chest complaints like asthma, serious kidney or liver disease, diabetes, lowered immunity and people who have suffered a stroke can also get one.

GPs may also recommend a flu jab for people who have had a transient ischaemic attack (TIA), sometimes known as a mini-stroke; multiple sclerosis and other degenerative conditions of the central nervous system.

It is estimated that around four million people in England under the age of 64 could benefit from a flu jab.

The Department of Health released the results of a survey to coincide with the launch of its flu vaccine campaign.

It showed that one in three people (34%) confuse the flu with a "heavy cold" and half believe in "old wives' tales" rather than following the advice of their GP when it comes to preventing flu.

Prof Salisbury said: "We are urging those at greater risk - including people suffering serious heart problems, asthma and diabetes - to get their flu jab from their GP. The jab can literally save lives."

The poll of more than 1,000 adults, also found that while 61% knew of the risks for older people, 24% did not know flu was potentially fatal for those under 65 in at-risk groups.

Gordon Lishman, director general of Age Concern, said: "Flu is a serious and dangerous illness that causes misery to thousands of people every year, and in some cases it can be fatal for older people. We would urge all older people to have the flu jab at the first opportunity."