Why is Boris Johnson calling for more NHS cash?

It won't be the first time that Boris Johnson has called for more cash for the NHS.

Depending on the flavour of your own views, his promise during the referendum of an extra £350m for the NHS was either an entirely sensible and publicly appealing promise of how we should spend the EU membership fees that may (eventually) come back to the country after we leave, or a classic piece of political sleight of hand.

Frankly, we have all discussed that one enough for most people's liking.

Labour is calling for an additional £5bn to be pumped into the NHS straight away.

But this week, even though he was not in charge of the NHS when I last looked, Mr Johnson is expected to make the call at cabinet for an extra £100m a week for the NHS in England, and a more vigorous approach to the politics of the service.

Sources close to him suggest the foreign secretary thinks "Number 10 is abandoning the territory".

He is not the only government minister who is worried that Theresa May isn't paying enough political attention to the travails of the health service.

Other Brexiteers, like Michael Gove, are understood to share some of his fears.

Health Secretary Jeremy Hunt is not, sources say, working in concert with Mr Johnson, but is also known to be privately making the case for more cash.

The health secretary is thought to share Mr Johnson's concerns

Others may well agree, even if Mr Johnson's likely intervention at cabinet might ruffle a few feathers.

A cabinet minister, not in the usual Brexit camp, told me "everyone says privately that something has to change," adding: "We have to offer a reason why we should run it (the NHS), not just be in a bidding war with the Labour Party."

Number 10 says the NHS was given "top priority" in the last Budget, with extra funding where other government departments' calls largely fell on deaf ears.

With no majority, and their limits on public spending, the government has little room for manoeuvre.

But growing numbers of Tory MPs are openly expressing their frustration with Number 10's handling of the NHS, particularly, the prime minister's response to calls for a cross party commission to tackle the long term challenges it faces.

There are several factors stirring the pot.

There is a desire among Brexiteers, not least Mr Johnson, to be seen to be at least trying to aim to keep the big promise they made during the referendum in 2016.

There is the genuine concern felt by MPs from all political parties, and prominent Tories, like Sarah Wollaston, who chairs the health select committee, about the future of the health service.

The NHS is always just about at the top of voters' list of priorities - and the perceived lack of action is heightening anxiety about Theresa May's leadership more generally.

The NHS is always a top priority for voters

One senior Tory MP told the BBC "we all know the problem - it is at the centre there is no decision making".

A former minister said "more and more people are saying, we can't have another year like this".

Even normally loyal MPs, like Nicholas Soames, are on somewhat itchy form.

After the former minister Nick Boles criticised Mrs May's "timidity" - saying the government was full of "boiled rabbits" (a phrase borrowed from George Orwell) - Mr Soames wrote on Twitter, 'where is the bold and brave, so far it is dull, dull, dull'.

Another MP described Theresa May unflatteringly as a "Soviet leader who goes up to the window to be seen but no one is quite sure if they are alive".

It doesn't seem likely that Mr Johnson's likely intervention at cabinet will suddenly provoke Number 10 to make a dramatic move on the NHS.

Money, and political capital in the Tory Party are in very short supply.

And just as there are cabinet ministers who may swing behind him in agreement, it is possible that his intervention may rankle others too.

Who knows, it's possible that the foreign secretary may (unusually, you might say) decide to keep his counsel.

Increasingly though it is harder for Theresa May to avoid this conversation. It's not just the NHS, but the prime minister and the Conservatives, that are under winter pressure.