One of the key battlegrounds in the forthcoming election is the National Health Service. The NHS, set up in 1948 and the brainchild of Labour health secretary Aneurin Bevan, was designed to offer care free to everyone at their point of need and financed entirely from taxation. However, it has proved very expensive to run and in spite of successive reforms it has struggled to balance its books.

It is one of the few state institutions that British people are genuinely passionate about, to the extent that an NHS bed ballet formed part of the opening ceremony of the 2012 Olympics.

I shed a tear.

A little excessive, perhaps, but the NHS is generally regarded as a credit to a civilised society and one of the greatest achievements of a great reforming government. The Conservative Party – which opposed its creation – struggles with the perception that it is not really committed to it.

Are they?

Yes, not least because it would be electoral suicide to be anything else. There are certainly differences in emphasis, though. A recent survey of 115 Conservative councillors found that 26 backed charging for some NHS services, 12 supported increased use of the private sector and six wanted to cut the health budget.

That doesn't seem exactly earth-shattering. After all, the NHS is very expensive.

In absolute terms, yes, it is – just over £113 billion in the last financial year, and just over £115 billion next year. That's around nine per cent of our total national GDP. However, it's not a vast amount by the standards of other countries. The USA hovers around 17 per cent, the Netherlands is around 11.7 per cent, France is 11.6 and Germany 11.3.

But ours is the best, isn't it?

Oddly enough, given how much we like to moan about it, arguably it is: the Commonwealth Fund did a comparative survey with 10 other countries including Australia, the US and major European nations and found that the NHS was most impressive overall, coming out top in terms of efficiency, effective care, safe care, coordinated care, patient-centred care and cost-related problems.

So it's cheap and effective, what's not to like?

Well, it isn't that cheap, and it isn't always effective, either. There is always the question about how much money a government is able to devote to it, and that amount is always less than a health service actually needs. There are particular pressures on the NHS because – uniquely among major economies – it is financed entirely through taxation, meaning that decisions about funding are always political. Furthermore, healthcare is getting more expensive all the time.

Why? I thought were were a lot healthier than we used to be?

You might like to think about that one.

Ah, we're healthier because we spend more money on healthcare.

Yes. And there are huge pressures on resources, simply because we're better at curing people, or at least at keeping them alive. More people are living longer with chronic conditions like diabetes, heart and kidney disease, which means that they're more expensive to keep going. Also, we can treat conditions that would have been fatal 70 years ago. That's good, but the treatments cost a lot. We're also picking up the bill for 'lifestyle' illnesses – too many people eat the wrong food, smoke and drink too much and don't exercise, and obesity is a major problem. It's been estimated that the NHS faces a £30 billion funding gap for the NHS by 2020 if things don't change. There's also the cost of not doing things: the NHS keeps people healthy and so it keeps them working and paying tax – and keeps them out of the social care system, of which more later.

That's rather alarming. But look, other countries do things differently: isn't there something to learn from them?

One idea is to move to an insurance-based system like the one they have in the US. However, in spite of the recent advances under the 'Obamacare' initiative which have seen around 16 million previously uninsured Americans get coverage, the US system is widely seen as an example of how not to do it. One of the criticisms of an insurance-based system is that it institutionalises inequality: you're treated according to what your insurers will pay for, rather than what your doctor thinks you need. It also locks a financial incentive in place both for hospitals and drug companies, which drives up insurance premiums. Obamacare is still fending off legal challenges and an incoming Republican president might scrap it.

Ouch. But there must be other systems.

Well, Australia has a combination of public health funding and private healthcare insurance, with a complicated system of subsidies. Other countries do it differently. But the argument for the NHS is that it is a genuinely fair system. On the other hand, that doesn't mean that everyone will always get every possible treatment imaginable. Healthcare is 'rationed', in the sense that some drugs are deemed too expensive to be worth the results they might bring. People with private health insurance could still get those drugs, so there is still an advantage to being wealthy.

I don't believe in privatising the NHS.

That's a good slogan which has been used very effectively by politicians. However, you need to think about what it means. If you're saying that you don't want to have to fork out every time you go to the doctor, fair enough. However, that isn't generally what's envisaged (though it has been seriously suggested that a modest charge for a doctor's visit might encourage self-reliance). Privatisation involves the NHS, or bits of it, paying private companies to do things because they'd be better at it than a huge and unwieldy body like the Health Service (it employs 1.6 million people, putting it in the top five of the world's largest workforces together with the US Department of Defence, McDonald's, WalMart and the Chinese People's Liberation Army).

Ah, right. But privatisation hasn't actually worked too well, has it?

Sometimes not. Having hospitals cleaned by private contractors has sometimes led to hospitals being dirty. But that is not a necessary consequence of privatising cleaning, it just means the contract has been badly handled. And getting private hospitals to do operations – at a price – doesn't necessarily mean that the operations will be done badly or that they'll be more expensive, though sometimes that has been the case. Some people believe on principle that the state should be running the whole show, but arguably the point is that the patient gets the best care, free at the point of need. But the argument is complex: competition doesn't always make things better or cheaper, private contractors will cherry-pick the most profitable areas of work, and even the tendering process for work is expensive and adds to costs. Labour says it will cap the amount of profit private contractors can make at five per cent – not enough to make it worth their while, opponents say.

Alright, so all the parties believe in the NHS – what are they going to do about funding it?

That's the question that they have been trying to avoid. The NHS said in its Five Year Forward View that of the £30 billion funding gap it faces by 2020, it would need £8 billion in extra taxpayer funding. The other £22 billion would come through efficiency savings, which former NHS chief executive Sir David Nicholson told Radio 4's Today programme was not achievable. The other elephant on the ward is the cost of social care – a separate budget from the NHS, but inextricably linked to it. That's the sort of care that keeps people in their homes when they're old and frail. The problem is that when the NHS fails – for instance, when waiting lists for knee and hip operations get too long – the cost of social care rises because people can't get to the shops, so end up in nursing homes.

So Labour wants to "join up services from home to hospital" and work on prevention and early intervention. They have promised an extra £2.5 billion a year to recruit nurses, GPs and midwives. The Conservatives say they'll also be "joining up services between homes, clinics and hospitals", and have guaranteed the £8 billion while refusing to say how the money would be found. The Lib Dems want to join up health and care funding at a national level, and says that their plans to deliver the extra £8 billion are fully funded.

You aren't really offering clear blue water between them.

The water is not very clear, or very blue. The parties all think that the Five Year Forward View provides the context for their commitments. The question is how these commitments will be funded. There are questions of principle – eg should excellent health care be paid for from taxation or through an insurance system? And there are questions that look like principle, but are often about management – like the privatisation debate. What is clear is that with all its failings (institutional arrogance, for instance, illustrated by its frequent attempts to silence whistle-blowers) the NHS is the fairest system we can find. So while rich people might be able to get better care by paying expensive insurance premiums to private providers, it is right and proper to spend a large part of the nation's wealth on supporting it.