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By coincidence, today is the last day at work for the boss of the entire civil service.

And just as Sir Mark Sedwill leaves his post at the head of Whitehall for the last time, another permanent secretary, Sir Jonathan Jones, leaves alongside.

On Monday, Downing Street and ministers were wrangling over just how controversial their new law to '"clarify" the divorce deal the government signed with the EU really was.

Twenty-four hours later, a secretary of state has admitted in Parliament that it will break international law in some ways.

The former prime minister, Theresa May, has blasted the government from the backbenches.

And it's clear that for Sir Jonathan, the government's own most senior lawyer, the changes that are proposed (a reminder: we still haven't seen the bill in full) push too far against the government's obligations under international law.

It's said to be unconnected, but another of the government's most senior lawyers, Rowena Rice, has also just left her post.

But the idea of passing legislation at home "notwithstanding" an international treaty - essentially setting aside a legal deal - is not completely unprecedented.

Brandon Lewis, the Northern Ireland secretary, tried to explain this point in the Commons, while some backbenchers' eyes rolled behind him. Yet it is certainly unusual, and in this context, deeply controversial.

And government insiders acknowledge that it will be seen by many, including some in the EU, as a "nuclear option" that could cause alarm.

It's another reminder that this administration relishes controversy.

And that it is willing to enrage opponents and push convention, if it means getting its desired result.

Whether you loathe the government's abrasive style or love its ruthlessness, far from seeking a peaceful conclusion to Brexit, for No 10 there are plenty of fights still to have.

And that may mean accelerating the number of top civil servants who are cleared out - or clear off of their own volition.

Six permanent secretaries - who head government departments - have gone now.

Given the importance of the principle of the rule of law, one former permanent secretary told me Jonathan Jones' departure is "absolutely massive, by far the most important yet".

And few at Westminster believe there won't be more to come.