Professor Jim Horne, of the Loughborough University Sleep Research Centre, said the tendancy to feel sleepy in mid-afternoon was probably a legacy of our distant past.

BBC: How we go to sleep

If snoring is combined with feeling sleepy during the day and experiencing pauses in breathing during sleep, people may be suffering from the more serious sleep apnoea - which affects 10 to 20% of snorers - and should see their GP.

BBC: Snoring cures success 'exaggerated'