Welcome to HSJ’s new Performance Watch expert briefing. Our new fortnightly newsletter will delve into the most pressing performance matters troubling system leaders and provide unrivalled insight into what they plan to do about them.

Oh to be a fly on the wall in Jeremy Hunt’s Monday meeting with the health service’s senior leaders next week following NHS England’s board meeting yesterday.

The NHS England has set out its message to ministers: either constitutional waiting times will slide, or cuts to other services are needed because the funding settlement in the budget means we can’t do it all.

The health secretary swiftly hit back. The NHS had been given a “significant [funding] increase” and the government was “absolutely committed” to all the constitutional waiting time targets, he told a King’s Fund event.

There may yet be deals done between government and the NHS leadership in darkened rooms.

But for the time being at least it appears the battle lines are drawn with the two sides set to slug out their differences in a fractious and public debate over the 2018-19 NHS Mandate, the document which sets out ministers’ asks of the health service.

Such a battle could move the mandate – thus far a largely ignored Lansley Act statutory formality – to centre stage in the debate over for the future of the NHS.

The messaging from NHS England at yesterday’s board meeting about which services could be most vulnerable to cuts was also interesting and worth further analysis.

Simon Stevens warned at the NHS Providers conference last month that ministers could be forced to publicly abandon legal waiting times guarantees, while improvements in mental health and cancer care could also be jeopardised

The debate around waiting times has so far focused on the 18 week referral to treatment electives target.

NHS England confirmed and arguably hardened its stance yesterday. “NHS constitution waiting times standards, in the round, will not be fully funded and met next year,” says the board’s NHS planning for 2018-19 paper.

However, the same paper also makes a potentially significant point about the accident and emergency four hour target, which has until now been the NHS’s key performance metric.

The word “realistic” (or “realism”) appears five times in the eight page document perhaps implying NHS England’s board view current expectations as not realistic.

The paper then says: “[It] will be important to set realistic plans for the growing level of emergency activity that hospitals and ambulance services will need to respond to next year.”

There is no suggestion that NHS England is angling for the four hour target to be scrapped. Indeed, urgent and emergency care was top of the list of services Mr Stevens said needed protection during the board meeting – the suggestion is the NHS must expect further resources to need to go into the emergency care system to maintain performance amid growing demand.

But, it is worth noting that NHS England appears to be, implicitly at least, questioning how realistic existing expectations around A&E are. This is especially noteworthy as it pledged only this year to return the system to compliance with the 95 per cent benchmark by next year.

As for the other protected areas, it is also worth noting that NHS England yesterday called for “planned investment” on primary care, mental health and cancer services should be protected.

This is despite Mr Stevens saying before the budget that it would be “increasingly hard to expand mental health services or improve cancer care” unless there was a significant funding boost.

I would not be foolish enough to guess which of the children could be in line to get shot first but the group of protected services appears to be becoming clearer.

Any lingering cordiality between NHS England and government has abated, and an intriguing but highly depressing battle has commenced about what services the NHS will and will not provide.