SO you’ve had a heavy night but you’ve slept it off and waited until all the alcohol is out of your system.

So you should be fine to drive, right? Well, maybe not.

According to a new study even when your hangover is one the wane and you’ve left enough time for the alcohol level to drop to zero, your brain is severely impaired.

The body metabolises booze at the rate of a unit an hour so, in theory, if you had 12 units (a bottle and a half of wine or six pints of beer) it should take 12 hours for you to get back to normal.

However, researchers at the University of Bath found that brain impairment can carry on even when all the alcohol in their system has metabolised.

So while you may pass a roadside test for alcohol level, you may not be capable of driving well.

The author of the study, Craig Gunn, said: "We found that hangover impaired psychomotor speed, short and long term memory and sustained attention.

"Impaired performance in these abilities reflects poorer concentration and focus, decreased memory and reduced reaction times the day after an evening of heavy drinking..

He also added that further research on alcohol hangovers needs to be carried out.

But it seems that even after the effects of booze appear to have worn off, you won’t be the sharpest tool in the box.