Reducing vigorous exercise by a few minutes a day raises the risk of cancer by 15 per cent, a study suggests.

It means choosing not to run for the bus or swapping trips to the gym for nights in front of the TV could prove deadly.

Researchers from University College London warn people should remain active throughout their life and not ease up as they age, as even small drops in activity can affect health.

Their latest work, published in the journal BMC Medicine, examined Britons' lifestyles and also used modelling to see how exercise was linked to cancer risk. The analysis included 59,218 people – 55 per cent female – with an average age of 61.7 from the UK Biobank, a database of half a million volunteers taking part in medical research.

Over an eight-year follow-up, 2,385 cancers occurred in the group. The experts looked at how long people spent sleeping, sedentary behaviour such as watching TV, standing and then any movement and at what intensity.

They found the more people moved, the lower their risk of cancer. For example, replacing 15 minutes of sleep or sedentary behaviour with 15 minutes of movement were each linked to a 2 per cent reduced risk of cancer. Conversely, swapping 30 minutes of movement of any intensity for 30 minutes of sedentary behaviour increased the risk by 8 per cent.

Dr John Mitchell, lead author from UCL, said: 'Our study showed that there's an increased risk of cancer for those who spend a lot of time sitting down.

'We also explored what might happen if people leading active lives reduced their levels of physical activity and found that they also face a higher cancer risk.'

Referring to the 15 per cent raised danger, he added: 'Our study showed losing two to three minutes per day of vigorous activity and replacing it with sitting down, sleep or light activity increased their cancer risk.

'Examples of vigorous activity – anything which elevates your heart rate and makes you sweat – include sport, rushing up the stairs and carrying home heavy grocery bags. The take-home message is that for people already leading physically active lives, it's really important to maintain that level of activity as you get older.'

Previous studies have found strong evidence that higher levels of activity are linked to a lower risk of several cancers – including of the bladder, breast and bowel.

The NHS say adults should aim for at least 150 minutes of moderate activity a week or 75 minutes of vigorous activity a week.

Examples of moderate activity include very brisk walking, everyday cycling or badminton. Vigorous activity includes hiking, jogging at 6mph or faster or tennis.