IF independence and Brexit are the great divisive issues, the unifying topic in British politics is the National Health Service. It is “the envy of the world”, the “greatest achievement of the welfare state”, the “closest thing the English [sic] have to a religion” (Nigel Lawson) and something which “will last as long as there’s folks left with faith to fight for it” (something Nye Bevan never said – but it’s now too late to dislodge the line, which actually comes from a play about him).

It’s not quite any of those things, but the British public often acts as if all these maxims were carved on tablets which should be handed out free of prescription charges. Otherwise we’ll end up like the US where, as is well known, everyone without an American Express gold card ends up dead in the gutter, where private ambulances heartlessly run over their bodies.

The NHS has always been a problem for the Tory party despite, or perhaps because of, the fact that it has been in power for most of the 70 years since its foundation, and consistently increased its funding. The NHS budget – in real terms – has gone from £12.6 billion to more than £140 billion, though precise figures are surprisingly difficult to nail down, because of changes in allocation between NHS and Department of Health totals, and the devolution of NHS trusts across the UK.

Under the Barnett Formula, for example, the 3.4 per cent announced yesterday translates into about £400 million for NHS Scotland in the first year, rising to about £1.6 billion. But we still don’t know whether we are dealing with DoH, NHS England or total UK NHS figures, though social care – a huge influence on NHS expenditure – is to be worked out separately in the exciting 10-Year Plan poor Philip Hammond is going to have to feed into his spreadsheets.

Anyway, as a proportion of GDP, NHS spending has gone from around 3.5 per cent to around 9 per cent; despite the period of “austerity” after the 2008 crash, the NHS’s tightest periods were just after its creation and during the Labour government of 1974-79. There is still a widespread notion that the NHS is Labour’s safe subject, just as defence and fiscal competence used to be regarded as solid Tory territory.

If the Conservatives have, as the Left constantly claims, a secret plan to starve the NHS of funds, they’re making remarkably little headway while, if the ambition is to privatise it by stealth, they’re taking forever about it. (Maybe because so much of it, such as GPs, has always been private anyway.)

The fact is that all parties have generally spent as much as they can afford on the NHS every year since it began, partly because it’s popular, and partly because the demands have risen inexorably with a growing and ageing population.

You might think that Theresa May’s announcement that the government plans to spend £20 billion more (around 3.4 per cent) over the next few years was a brilliant coup. It’s more than Labour had committed themselves to spending – indeed, Emily Thornberry stonewalled during a TV interview rather than promise to match it. It’s also more or less exactly the amount identified as shortfall by NHS pressure organisations, and groups such as the Institute for Fiscal Studies and the King’s Fund.

But that is to reckon without Mrs May’s political superpower, which is a sort of reverse Midas touch. On Sunday these funds were going to come out of the “Brexit dividend” but in her speech yesterday she acknowledged that it will require additional taxes. The trouble for the Prime Minister is that lots of people don’t think there will be a Brexit dividend – au contraire, as Michel Barnier’s translation earpiece would no doubt put it – while the Conservative manifesto promises lots of tax cuts.

The personal allowance is supposed to increase substantially. Reducing higher rates of tax and corporation tax are stated priorities. The Prime Minister looks as if she’s stolen the Labour Party’s clothes only to discover that she’s not got the T-shirt that says “I love the NHS the most”, but Jeremy Corbyn’s tatty grey nylon tracksuit, which gives the impression that you’re offering the Moon on a stick without the faintest idea where the money’s coming from.

The critical problem, as, predictably, those within the NHS or with a vested interest in it have quickly pointed out, is that even if the money materialises, it’s only more or less in line with average previous spending and minimum future requirements, and doesn’t prepare for the greater costs expected as a result of the UK ageing demographic.

That will be true even if there is a Brexit dividend – and there are good reasons to think there will be at least some. There will be substantial amounts of money not going to Brussels, after all, even if there’s a big exit bill and plenty of other areas (farming, education, development projects) which expect government to make up the shortfall from the bits we used to get back.

If (some hope) the government handles future trade opportunities sensibly, the cost of food and other imports ought to fall dramatically, while exports could soar. This is all possible, even if the economic doomsayers who have so far always been wrong deny it. That doesn’t mean, however, that it’s probable.

In any case, buckets of money wouldn’t be enough, and we have the evidence of the Blair/Brown governments, which greatly increased NHS spending, to prove it. Productivity in the NHS reduced the more taxpayers’ money it got, while it increased during the period of austerity (necessity being the mother of invention).

This is in part a tribute to the commitment of many NHS staff, but it doesn’t make them saints either. There is still colossal waste in the “shoestring” NHS (which gets about the same overall spending as the average for developed nations, on a par with Canada, Finland and Ireland, but employs many more people and has generally poorer health outcomes for patients). Cutting the chaotic procurement budget by just one per cent, for example, could pay for 4,000 junior doctors.

A real plan for reform matters as much, and almost certainly more, than money. But if Mrs May can’t say where the latter’s coming from, why have any faith we’ll get the former?