One in two smokers hide their habit from friends, family and colleagues, revealed a recent report.
Women were the main offenders with more confessing to keeping their habit a secret.
They were also better at keeping their habit hidden with more than a third hiding it for more than 5 years.
Researchers who polled 2,000 smokers found 52 per cent regularly enjoy a sneaky fag out of sight of disapproving eyes.
That means around 5.2 million smokers manage to find time for a quick puff outside Britain's offices or back gardens.
A belief others would be 'disappointed' or 'angry' if they found out was the most common reason for keeping their habit a secret, closely followed by 'embarrassment'.
The figures emerged in a study by Nicorette to launch their QuickMist Mouthspray.
Spokeswoman Caroline Swinhoe said: ''We know that when smokers stop smoking their body misses the nicotine from cigarettes and they may experience unpleasant cravings.
''It is often these overwhelming cravings that contribute to smokers failing to quit.
''So, finding a method to tackle cravings quickly could be the key to unlocking smokers from their dependency.''
The study found nearly 40 per cent of secret smokers confessed they hide their habit from others on a daily basis, while 32 per cent admitted living a lie for five years or more.
A handful admitted they retired to their car or garage for a fag, while others admitted visiting friends who smoke to have a cheeky cigarette.
One in five secret smokers said they were 'very weak' when trying to resist their cravings for a cigarette.
The survey also found most people give in to a cigarette within 30 minutes of their cravings starting.
It also emerged more than 60 per cent had tried to quit but found the cravings just too bad.
Almost one in five had experienced trouble sleeping because they needed a cigarette while a further 30 per cent admitted having travelled five miles or more in order to get their hands on a cigarette.
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