Boris Johnson's secret pro-EU article has been revealed

An article written by Boris Johnson in which he outlines why Britain should remain in the EU has been revealed.

Johnson, who campaigned fiercely in support of Brexit, wrote the unpublished article just two days before announcing his alliance with the Leave camp.

In the pro-EU article, published in a new book and the Sunday Times, he supported membership of the free-trade zone and insisted that Britain's membership of the 28-nation bloc is a "boon for the world and Europe."

"This is a market on our doorstep, ready for further exploitation by British firms," he wrote on February 19.

"The membership fee seems rather small for all that access. Why are we so determined to turn our back on it?"

The foreign secretary also foresaw the "economic shock" that has since seen the pound fall to historic lows.

The previously unseen comments have been published in a new book by the Sunday Times political editor, Tim Shipman: "All Out War: The Full Story of How Brexit Sank Britain's Political Class."

In the weeks running up to the referendum, the foreign secretary became one of the most prominent and recognisable Leave campaigners.

According to The Guardian, sources close to Johnson claim he wrote his article as a way seeing if the pro-EU argument had any ground and dismissed his article as soon as he had finished.

The article also urges voters to "think of the future." Johnson wrote: "Think of the desire of your children and your grandchildren to live and work in other European countries; to sell things there, to make friends and perhaps to find partners there."