The average lunch break now lasts just 22 minutes – a third less than six years ago.
The research found that nearly one in five workers never leave their desk during lunchtime, despite warnings that being sat for eight hours a day kills as many people globally as smoking.
Fitness experts said lunchtimes were being squeezed by work pressures, with figures showing the average lunch break has fallen from an average of 33 minutes in 2012 to 22 minutes today.
The poll of more than 800 workers by not-for-profit health body ukactive and Sodexo, found most wanted to exercise more, but three quarters said their workload got in the way.
Just one in five reported cycling or walk to work, while three quarters said they did no physical activity during their lunch break.
And 77 per cent said corporate gym memberships would have a positive impact on their physical and mental health, while almost as many said shower facilities and compulsory lunch breaks would boot their health.
British people lose 18 days a year from consistently not taking their lunch break.
Workers reported reasons for missing their breaks included excessive workload, unexpected tasks and not enough variety of nearby dining options.
The health risks of not taking a lunch break are well-known by medical professionals.
Ukactive chief executive Steven Ward said: “These figures are a shocking indictment of modern workplace cultures, where employees increasingly find themselves tied to their desks and screens all day.
“Our research shows staff believe in the benefits of being more physically active but don’t feel they have the time – employers should heed these warnings if they want to encourage their teams to be more productive.”
Research has found that sitting for eight hours a day could increase the risk of premature death by up to 60 per cent.
The Lancet study found that one hour’s activity daily could offset the potential harm of a day spent at the desk.
But almost one in four adults in England fail to achieve even half an hour of activity a week.
Last week, the Health Secretary urged employers to give workers standing desks and get staff on their feet for meetings.
Matt Hancock called on businesses to help employees to build activity into their days, in a bid to counter deadly sedentary lifestyles.
The health secretary said he uses a standing desk – finding it boosted his increased his activity levels, and boosted productivity.