Warnings of an obesity timebomb and the encouragement provided by London's winning bid for the 2012 Olympics appear to have spurred the British public into becoming sportier citizens.

Three-quarters of adults have turned their back on the couch potato lifestyle and take part in exercise at least once a week, according to research published today.

The survey by the market research company Mintel reveals that 74% of people aged over 15 exercise at least once a week, compared with 70% two years ago. The proportion exercising more than once a week has increased, from 48% to 52%.

Among those who exercise once a week, swimming is the favourite activity, enjoyed by 23%, followed by hiking and rambling (20%). Keep fit, aerobics and stretch, weightlifting and gym, jogging and cycling are undertaken by 18%.

Swimming and cycling are the most popular pursuits among those who exercise two or three times a month.

Jogging is the favourite for those who exercise more than once a week, with 65% taking part regularly.

The findings were described as encouraging by Roger Draper, Sport England's chief executive. "Sport England have the demanding target of increasing participation in sport and physical activity by an average of 1% year on year."

To get an even clearer picture of the physical state of the country, the organisation is embarking on the Active People survey, the biggest national participation poll undertaken.

"The realisation of our Olympic vision, tackling obesity and helping to create more cohesive communities all rest on establishing a clear understanding of how physically active a nation we are," Mr Draper said.

Silvia Bartels, the consumer insight manager at Mintel, said: "While more consumers are playing sport regularly, an increasing proportion of them are opting for activities that cost nothing to take part in.

"Clearly the cost of exercising is an increasingly important factor when it comes to keeping fit, and may be at the root of the growth in popularity of sports in which free play is the norm, for example, cycling, hiking, rambling and jogging.

"Previous research has also shown that many British people are buying home exercise videos and their own dumbells so that they can exercise at home while keeping costs to a minimum."

The number of regular exercisers not paying to stay in shape has risen from 34% in 1998 to 39% in 2005, and only 20% of adults pay more than £200 a year.

Almost a quarter of the sample of nearly 2,000 people had taken part in a sporting event for charity. Two in five believe such events are "great fun as well as an ideal way of raising money", while 18% said charity events were a good way to push themselves athletically and achieve personal goals.

"In an era of increased obesity and government encouragement for a healthier nation, more could be done to use fundraising sports events to increase participation in an attempt to improve the general levels of fitness in Britain today," Ms Bartels said.

Sports for good causes, Mintel International Group www.mintel.com