The secret to a long and happy marriage could be having separate beds, an expert on sleep claims.Not only will a couple escape arguments over duvet-hogging and fidgeting, but they will have a proper night's rest.This will have a huge impact on both their health and the relationship as poor sleep increases the risk of stroke, heart disease and divorce, said Dr Neil Stanley.The consultant, who set up sleep laboratories at Surrey University, said: 'Poor sleep is bad for your physical, mental and emotional health. There is no good thing about poor sleep.'If you sleep perfectly well together, then don't change. But don't be afraid to relocate.' If a husband or wife snores, twin beds might not be an option either, and they should sleep in separate bedrooms, he told the British Science Festival.Dr Stanley, who follows his own advice and sleeps in a different room to his wife, said that double beds are just not conducive to a good night's sleep.He said the tradition of the marital bed began with the industrial revolution, when people moved into cities and found themselves short of living space.Before the Victorian era it was not uncommon for married couples to sleep apart.He said that now the British way is to have a 4ft 6in double bed. 'A standard single bed is 2ft 6in or 3ft, that means you have nine inches less sleeping space in bed than your child does in theirs.'You then put in this person who makes noise, punches, kicks and gets up to go to the loo in the middle of the night, is it any wonder you are not getting a good night's sleep?' He added:'Poor sleep increases the risk of depression, heart disease, stroke, respiratory failure and increases the risk of divorce and suicidal behaviour.'A recent large- scale Japanese study concluded that seven and a half hours of sleep a night is optimal for good health.A third of British adults regularly have fewer than five hours. Dr Stanley's advice follows studies at Surrey University on the impact of tossing and turning on sleeping partners.When one partner moves in his or her sleep, there is a 50 per cent chance the other will also change position.Despite this, couples are reluctant to sleep apart, with just 8 per cent of those in their 40s and 50s bedding down in different rooms.Separate bedrooms are much more common in old age, with more than 40 per cent of those aged 70-plus sleeping apart.This could be because long-established couples feel more secure in their relationships.They may also find it easier to bring up the touchy topic of one moving out of the marital bed and could also be more likely to have a spare room than a younger couple.Dr Stanley said the argument that it is comforting to sleep beside someone else holds little water.He said: 'Sleep is the most selfish thing we can do. People say that they like the feeling of having their partner next to them when they are asleep. But you have to be awake to feel that.'We all know what it is like to sleep in a bed with somebody and have a cuddle. 'But at one point you say, "I'm going to go to sleep now".'Why not at that point just take yourself down the landing?'Intimacy is important for emotional health. But good sleep is important for physical, emotional and mental health.'Getting a good night's sleep is something we should all aspire to.'