Apple watches could add two years to your life, a major study suggests.

Research on 400,000 adults found that those who used fitness trackers linked to reward schemes saw activity levels increase by more than a third.

The findings - from the largest ever study of behavioural technology - amount to around an extra two years’ life expectancy, insurance experts said.

Participants with an Apple watch made monthly payments of up to £12.50, depending on their activity levels - with nothing at all to pay if monthly exercise targets were achieved.

Those with the trackers managed 4.8 days activity a month on average - compared with 3.5 days among those without such devices, the independent study by Rand Europe found.