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Now he's gone and done it.

For a long time it had been clear Boris Johnson was not happy with the prime minister's Brexit strategy.

His dissatisfaction was more than just the odd off-colour remark, although goodness knows there were enough of those.

His departure is a huge story and turns what might have been a couple of days of significant turmoil, into a significant crisis for Theresa May and the whole Brexit project.

He was Brexit's main cheerleader, the politician most associated with making it happen, and one of the best known politicians in the country, for good or ill.

It's enough of a mess on its own.

But a well-connected source has just told me it could be more serious than that.

They said it is a concerted push to force the prime minister to drop her Chequers compromise.

"If she doesn't drop Chequers there will be another," they said, "then another, then another, then another."

But if she can't force a compromise through her party that itself took months to stitch together, the prime minister's authority would be significantly diminished.

As Mr Johnson is hemmed in by paparazzi and camera crews outside his official residence that will soon be no longer his home, Theresa May is also a hostage with no obvious means of escape.