Oddly enough, London's mayor will have been cheered to spark a sell-off in the pound when political colleagues barely raised an eyebrow on skittish markets.
Here's what was probably going in that famous blonde head over the past few days.
This referendum is not about Europe – it's about what it means to be a British Conservative.
The incredible number of undecided voters means this must be an information-led campaign.
Michael Gove, Chris Grayling and Theresa Villiers head straight for Vote Leave HQ after cabinet meeting. As does the Mayor of London.
A specialist in EU law reads the fine print, so you don't have to.
Already over-indulged, Britain continues to demand special status in the EU. Is it worth it?
Europe's directly elected chamber is a tangled web of conflicting interests. But few want the Brexit debate to rumble on any longer than necessary.
Labour's shadow foreign secretary says leaving the EU would play into Russia's hands. Ordinary Brits worry more about their jobs.
The British PM thinks he has a deal to avert a Brexit? The rest of the union has far more pressing problems to think about.
There are almost no scenarios under which the UK could be completely independent from Brussels. No wonder the out campaigns are so vague on the details.
The credit-ratings agencies are already circling to cut the UK's grade if it votes to leave the EU. Here's how their calculations work, and what we should do about it.
Better hold off on booking that summer holiday to Europe.
Troubles in the eurozone can be viewed as a continuing fallout to the 2008 global crisis.
New research shows that the government's welfare proposal is out of step with reality.
The prime minister will have no choice but to pour all his heart and soul into the EU referendum.
It has taken a long time to write, but the PM still hasn't produced an entirely realistic plan for reform.
There are two groups vying to lead the Brexit camp but only one can become the official lead campaign.
The 'In' campaign has started on the back foot. Here's what it needs to do to get going.
The Bank of England has emphasised the overal benefits that membership of the EU brings Britain. But also warns of its risks.