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This bedroom is a battleground. Morgan's 17, and like most other teenagers, she struggles to surface.

Noelle Delaney, Mother:

Some days it is very difficult…you know I have to go in there two, three times. I have been known to pull her by her feet out of her bed.

Morgan Delaney, Student:

It's too early to get up in the morning, especially in the winter when it's quite dark out. It just seems like you're getting up in the middle of the night, you just want to be back in bed.

And that's why sleep scientists studied Morgan and her friends for two weeks. These wrist-mounted sensors monitored their every move – waking and sleeping.

Analysis of that data surprised the scientists. They found that consistently the teenagers get just six and a half hours sleep a night. Most adults need at least eight. When the clocks moved forward to British Summer Time the youngsters got even less – just six hours a night.

Joanne Bower, University of Surrey:

You've got something inside you called your circadian rhythm [body clock] which insures the same thing happens the same time every day and one of those things is the secretion of melatonin which is the hormone that makes you sleepy. Now for an adult you expect that to be early evening, in teenagers it happens much later so even if you put your teenager in bed at say ten at night it may be that they don't secrete their melatonin until midnight, one o'clock, so they're staring at the ceiling just not sleepy.

Consistent sleep deprivation can affect concentration, memory or even mood. The scientists behind this study say more research is needed because, like Morgan, most teenagers have busy lives - what they're not getting is enough rest.