Boris Johnson's former rugby coach says he's always been clever and is a bit of a rebel. 

The eccentric politician's tipped to be named Theresa May's successor as prime minister and Conservative party leader tonight.

Kiwi Ian McKinnon remembers his time as a 14-year-old Boris' rugby coach, while a deputy headmaster at the prestigious Eton College in London.

He told Heather du Plessis-Allan Johnson stood out then just as much as he stands out today - and has unlikely changed over the years.

"I can remember him arriving late to most things he was expected to be at, gown flying in one direction and a flock of blond hair flying in the other."

McKinnon says that Johnson was a robust forward, defying the reputation of his fellow 'colleger'.

He says that no matter what people think of his politics, Johnson has always been clever. 

"He's very clever, he's a classicist, he's a Latin and Greek scholar. He was clever at Eton."

McKinnon expects that Johnson will find himself in a difficult situation when it comes to trying to solve the crisis of Brexit. 

Several cabinet ministers are expected to quit or be be removed during the leadership change, with many protesting the fact Johnson has committed to leaving the European Union by October 31, deal or no deal.

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McKinnon says that will put a lot of pressure on Johnson.