The National Health Service (NHS) in England is at the centre of a big political row about its reform. It's often said to be the third biggest employer in the world, after the Chinese army and Indian Railways. But is that really true?

It's an incredible claim, given how much smaller the UK is than China or India.

And indeed, it is not true.

Sizing up the world's biggest employers and compiling a list of the top 10, the NHS is revealed to be the fifth largest, with 1.7 million workers across England, Wales, Scotland and Northern Ireland.

McDonald's makes it into fourth position, with 1.9 million employees. However, 80% of the restaurants are franchises so, strictly speaking, 1.5 million of these people are employed by other companies, although they all wear the uniform.

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Third is the US supermarket chain Walmart, which employs 2.1 million staff - including almost 200,000 who work for the Asda supermarket chain in the UK.

Second place goes to the Chinese military - the People's Liberation Army (PLA) - with forces numbering 2.3 million.

And the top spot is taken by the US Department of Defense with a cool 3.2 million-strong workforce.

Why is it so big - and so much bigger than the second-placed Chinese military?

In truth, making these comparisons is fraught with difficulties.

The US Defense Department, with its headquarters at the vast Pentagon building in Virginia, is keen to boast that it's one of the world's largest employers and includes civilian support staff in its numbers.

Image caption The Pentagon is said to be the largest office building in the world

Getting a comparable figure for the Chinese military is near impossible.

The figure of 2.3 million which puts it at second place in our list includes active forces only - not civilian staff, like the US figure.

And that actually makes it the largest active military force in the world, according to Military Balance, an annual assessment of military capabilities around the world published by the International Institute for Strategic Studies in the UK.

If you were to count only active forces within the US Department of Defense, it would number 1.6 million people and slip to seventh place in our list.

If numbers for its civilian staff were known, it is possible the Chinese could come much closer to the US, and maybe even overtake them.

But it is not a straightforward exercise even to separate who is civilian and who is military personnel - the two forces are structured and organised completely differently.

"There are a number of organisations within militaries - you have active forces, reserve forces, civilians, and also those that might be working as contractors - so it depends really what you're trying to count when you look at headline numbers," says James Hackett, the editor of Military Balance.

"What we try and do is look at active service personnel, so those in uniform who are capable of operating on behalf of the state to fulfil the national security concerns of the militaries.

Surprisingly, [the NHS] also has more workers than Indian Railways

"One reason that the PLA is large compared to other militaries stems from its composition as a mainly conscript-based force. Now other militaries in the West and across the world have moved to volunteer corps."

The NHS might be lower in the global pecking order than people think but it is still big.

Technically, however, it could be said the NHS does not operate as a single employer.

Many staff are employed by individual hospital trusts and primary care trusts, while GP surgeries, for example, are run and owned by one or more partners who are contracted to provide general NHS medical services.

But setting that aside, it is bigger - just - than the state-run China National Petroleum Corporation, which has around 1.6 million employees and operates in 49 countries.

It's also bigger than the State Grid Corporation of China, which ranks seventh in our list with 1.5 million staff.

Surprisingly, it also has more workers than Indian Railways, which is popularly thought to be in the top three of the world's biggest employers, but actually languishes in eighth place.

"Languishing" with an admittedly whopping 1.4 million-strong workforce - and with plans to recruit an extra 100,000 staff this year.

And it's still one place ahead of the Indian Armed Forces, which has 1.3 million people in its active forces.

Image caption Most of India's armed forces are in the army

The reason China's railway operation does not make the top 10 list is because it's split into various separate entities.

But Chinese operations do dominate the top 10 list.

Number 10 on the list - behind the Indian Armed Forces - is Hon Hai Precision Industry, better known by its trading name, Foxconn.

This Taiwanese electronics producer, which has 1.2 million employees, makes well-known products like the Apple iPad in its vast factories in China, where hundreds of thousands of people work.

It became notorious in 2010 when news spread that 10 of its workers had committed suicide.

Although these deaths were tragic, an understanding of how massive an employer the company is makes you realise that this isn't the shockingly high number it seemed.

Suicide rates in China have been put at 15 per 100,000 people per year. The controversial Foxconn factory employed around 400,000 people.

Ten suicides per 400,000 people isn't unusually high. It's unusually low for China.