Sir Winston Churchill's bravery in leading Britain during the Second World War may have been down to him suffering 'short man syndrome', a new book by Boris Johnson has claimed.

The Mayor of London says that with the wartime prime minister standing at just five feet six inches tall, there is evidence to suggest he was driven to succeed to prove a point to bigger bullies at school, who teased him for his height.

So-called 'short man syndrome' has been described by scientists where short men overcompensate for their lack of height through acts of aggression.

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A new biography of wartime leader Sir Winston Churchill by Boris Johnson suggests he may have suffered from 'short-man' syndrome

The Mayor of London says there is evidence to suggest he was driven to succeed to prove a point to bullies at school, who teased him for his height

It has long been associated with some of history's most notorious tyrants, including Adolf Hitler, Napoleon, Mussolini and Stalin.

And in Mr Johnson's new biography on Churchill, who was two inches shorter than Hitler, he suggests the syndrome was what spurred him on to tackle bigger bullies.

In the book, serialised in the Telegraph, Mr Johnson writes: 'Who else was 5 foot 6 or under? Some of the biggest tyrants and creeps in world history: Augustus (5 feet 6), Napoleon (ditto), Mussolini (ditto) Stalin (teensy at 5 feet 4). Hitler was only 5 feet 8.

'All these characters have been associated with the over-compensatory aggression that is sometimes referred to as 'short-man' syndrome; and there is some evidence, at least on the face of it, that Churchill did, too.'

At five foot eight, Hitler, left, was two inches taller than Winston Churchill. So-called 'short-man' syndrome is often referred to as Napoleon Complex, named after Napoleon Bonaparte, right, who was five feet seven

The new book, called The Churchill Factor, took the author over a year to research and will be published later this month ahead of the 50th anniversary of the leader's death.

In it Mr Johnson also explains how Churchill's early life as a pupil at the prestigious Harrow School may have led him to show he was made of stern stuff after being bullied for being a 'runt'.

He explains that Churchill was not in the Harrow football team, the school's more violent version of the game, or the cricket team and even ran away from other pupils on one occasion when they threw cricket balls at him.

He also suggests that he probably would have been picked on for his lisp and speech impediment too.

Mr Johnson, who himself is five feet ten inches tall, adds: 'Churchill's bravery wasn't something he just put on. It wasn't a mask he struggled with. He was made like that. The spirit of derring-do just pumped through his veins, like some higher-octane fuel than the one the rest of us run on. Nothing could stop him.'

However, Mr Johnson explains that what sets Churchill apart from other 20th Century leaders was his 'greatness of heart' and his ability to be immensely compassionate.

He points out that when Churchill's mother decided to sack his nanny, he used his small income to give her financial support as he was so appalled.

Studies into so-called short-man syndrome say that society's obsession with height forces smaller men to overcompensate by becoming chippy, more aggressive and - in extreme cases - lust power.

However, some have questioned whether the syndrome, sometimes called Napoleon complex after Napoleon Bonaparte is real.

Historians have also pointed out that at 5 feet 7, Napoleon was around the average height for his day.

Mr Johnson also points out that tyrants Mussolini, left, and Stalin, right, have also been associated with short-man syndrome

Meanwhile Mr Johnson has also said he believed the wartime leader would have approved of Parliament’s decision to back air strikes on ISIS.

He made the comments after revealing thousands of terror suspects in the UK are being monitored by the security services.

'I think he would be appalled by the spectacle of these cowards executing journalists, and I think he would have wanted to do something to set them back a long way, and if need be, to neutralise them altogether,’ Mr Johnson said.