Tanker drivers, teachers, Tube drivers - 2012 has been dominated by the threat of key workers striking in the UK. But is it possible to identify which group of workers is the most vital?

Tanker drivers are still locked in negotiations with employers, weeks after speculation about strikes caused panic buying and long queues on petrol station forecourts.

The episode brought back memories of the fuel crisis of 2000 and raised concerns about how dependent the UK is on a small number of strategically important workers.

Similar worries arose when it was reported that Tube drivers had reached a highly advantageous pay deal for working during the Olympics.

And teachers are threatening to strike this summer in a move that will force some parents to take time off work.

Such disruption raises the question of which group of workers the country couldn't do without. So how would one go about judging who the UK's most essential workers are?

One test - obvious in a free market economy - would be pay.

"The essential workers are really the entrepreneurs creating the wealth which is used to pay for public services - if they left, there wouldn't be a strike but there would be a brain drain," says Richard Wellings, deputy editorial director of the Institute of Economic Affairs.

But not everybody is convinced.

It's unlikely that if Tesco workers went on strike, Sainsbury's workers would also be on strike Tim Leunig, LSE

"You could argue that the people who are most essential are those who are the best paid," says Dr Tim Leunig, an economic historian at the London School of Economics. "This would mean hedge fund bosses. But that argument is obviously bonkers."

Then there's statutory regulation. There are a few jobs that are deemed so crucial to society's smooth functioning that workers are banned from striking.

These include armed forces personnel, the police and prison officers, although the association representing the last of these is understood not to regard the ban as binding.

But ask many people which workers are the most vital and you might get a list of the "life and death" staff - doctors, emergency workers, and those who ensure there are adequate supplies of food and water.

While they are not banned from striking, these workers have limited room for exploiting their power.

"Doctors don't strike. If people died in A&E because they'd walked out they would lose all the moral highground," Leunig says. It's a similar story with firefighters who went on strike in 2002 and were replaced by the Army's ageing fleet of green goddesses. Although in theory firefighters withdrew their labour, in practice they were prepared to respond to serious blazes.

Another factor to quantify a worker's strategic value is how easy they are to replace. If there was a walkout by cleaners, it might cause initial disruption, but temporary staff could easily be drafted in.

Image caption Speculation over a tanker driver strike had immediate effects

That's not the case with pilots or air traffic controllers, although in the 1980s US President Ronald Reagan managed to break the latter's strike with help from the military. Pilots are very difficult to replace as "you can't just bring in managers to fly the planes", says Andy Cook, chief executive of Marshall James, employee relations advisers.

Their absence could shut down an airline, he adds. If UK Border Agency staff strike, there is also the potential for travel chaos. And yet a strike in November last year reportedly failed to cause significant delays after civil servants filled in.

Baggage handlers need to be security cleared to work around aircraft. The process of going through the necessary checks might take several weeks, meaning it would be hard to recruit new staff quickly.

But, of course, we already know what happens when all flights are grounded. The Icelandic volcano episode in 2010, which saw flights cease for six days was widely described as "chaos".

But while the disruption to holiday-makers, business travellers and the small amount of food that comes by air would be significant, the major consequences would primarily be long-term damage to the economy and tourism, rather than immediate privation.

Apart from water, the most immediate privation that is easily envisaged is shortages of food. So how essential are Britain's grocery shop workers?

"If the people working in every food shop went on strike there's going to be trouble," says Leunig. "But it's unlikely that if Tesco workers went on strike, Sainsbury's workers would also be on strike."

Strikes recent and pending In June 2011 public sector workers went on strike in protest against proposed reforms to pensions

In November 2011 more than two million public sector workers went on strike, affecting medical services, transport and schools

In March 2012 there was panic buying over the threat of tanker driver strikes

In April 2012 the NASUWT teachers' union called for strike action against "ideologically driven attacks" on state education

However, in the case of the tanker drivers, the whole sector is threatening to strike. Therefore, the ability to cause disruption through collective - usually union - action is a crucial factor.

And what of the people who grow the UK's food? Unlike their French counterparts, British farmers rarely take to the streets.

They don't have an "iron grip" on the country's access to food these days, says Dr Neil Lee, senior economist at think tank the Work Foundation. There is a long time lag between growing the food and it reaching the shelves so any impact of a stoppage would be delayed.

Crucially, the UK imports about 40% of its food and this could be increased when there is a dispute. This might suggest that, in terms of immediate privation only, it is delivery of food rather than actual growing of it that is most vital.

Transport jobs have perhaps the greatest potential for disruption. Hauliers picketing refineries in 2000 created the first serious crisis for Tony Blair's government - with fuel running out at petrol stations.

The problem became so serious that hospitals were affected and supermarkets were beginning to run out of certain fresh goods.

The government later created the Civil Contingencies Secretariat to plan for this type of event. Its first head, Mike Grannatt, says the fuel crisis demonstrated how much disruption could be caused in a highly networked society.

It also showed the importance of fear and the public mood. While there was enough food to feed the nation, stocks of symbolic items like bread were running low. "The psychological effect of not being able to buy fresh bread resulted in people getting worried."

Tube workers are another group which is seen as vital to keeping London functioning. Without them, the Olympics would descent into transport chaos. This helped the unions extract generous allowances for working during London 2012. It's been widely reported that the highest paid tube driver now earns £61,218.

Image caption Tube strikes have caused chaos in the past

Wellings says society should not view Tube and tanker drivers as essential. He believes the concept of key workers is distorted by the modern obsession with health and safety regulations.

"Tanker or Tube drivers can be replaced with minimum training - Tubes pretty much drive themselves," Wellings says. "But artificial regulations, created by red tape, means they have to be certified, which creates barriers to entry. We are only talking about weeks of training - it's not years like it would to be a brain surgeon."

Of course, Tube drivers disagree about the safety of driverless trains, with union Aslef pointing to an incident last month at Finchley Road station in which a driver saw the hand of a boy reaching up from the track. The train's systems had said that it was safe to proceed.

And if driverless trains, why not pilotless planes? Most planes fly themselves and rarely need intervention from the pilot, Leunig argues. But their jobs are safe for the moment as passengers need the reassuring presence of a captain with gold epaulettes, he says.

Pilots are unlikely to accept that they are surplus to requirements. The crash of an Air France Airbus in 2009 prompted debate over how much of the blame for the crash could be put down to a failure of the plane's computerised systems as against pilot error.

In any case, whatever the debate over automation, even the driverless Tube would not be available in time for the Olympics.

Water, gas and electricity are all essential services. And in the old days before privatisation, workers in these industries had huge bargaining power, says Gregor Gall, professor of industrial relations at the University of Hertfordshire.

In 1970, electricity workers began a work to rule. It took just eight hours for a serious breakdown in the supply of electricity to occur.

The internet is becoming like electricity, like water - it touches all parts of the economy Paul Zwillenberg, Boston Consulting

Later came the three-day week which brought down Edward Heath's government. Today, though, it would be hard to shut down the supply of power, Gall believes. "If a group of workers at one station take action, you could still get it from another."

Miners used to terrify governments, says Lord Armstrong, a senior civil servant who advised prime ministers between 1970 and 1987. Prime Minister Edward Heath called an election in reaction to a miners strike to ask the nation "Who governs Britain?", the miners or his government. He lost the election.

The year-long strike by miners in 1984 was one of the defining battles of Margaret Thatcher's time in Downing Street. Today, the UK has shifted towards gas, and much coal comes from abroad.

Coal can also be stockpiled in huge quantities, something that affected the outcome of the 1980s strike.

Oil isn't as easy to stockpile, Leunig suggests, and there are plenty of other sectors where stockpiling is impossible.

Gas workers on platforms in the North Sea have not inherited the power of the mineworkers. Last year the UK imported more gas into the UK than was produced in the North Sea, notes Michael Bradshaw, professor of human geography at Leicester University.

Teachers are under the spotlight after the two biggest unions voted for strikes which could hit schools across the UK this summer. The country got a taste of such disruption last November, when a day of co-ordinated action with other public sector workers over pensions closed two-thirds of UK schools.

But while experts say striking teachers don't tend to present a big economic problem, many parents are inconvenienced when faced with childcare issues or having to take unpaid leave. Disruption doesn't just have to be economic.

For Leunig, teaching illustrates the difference between short-term crisis and long-term drain on the nation.

By going on strike, teachers do not bring the country to a standstill but a prolonged dispute would cause serious harm to the next generation.

Image caption Police leave in the capital is sometimes cancelled ahead of public sector strikes

"If they went on strike for 10 years you'd have a generation of 15-year-olds not able to read 'the cat sat on the mat'. It's a facetious example but there's a serious point too," Leunig argues.

When all else fails, governments can bring in soldiers, as was reportedly planned during the tanker driver dispute.

Col Richard Kemp, a former member of Cobra, the government's emergency committee, says there are only two things that would prevent the Army getting involved in a strike.

For example, a task may be too technically demanding or the military may be completely committed elsewhere. This summer the military will be dealing with the logistical demands of operations in Afghanistan and security duties at the Olympics.

In the 1970s and 1980s, the armed forces emptied rubbish and put out fires. The Army would be able to keep schools open if called upon. They might even relish the task of instilling a bit of discipline into the youth of today, Kemp says.

But teaching is not seen as essential in the same way as fighting fires or driving tankers. And politically it would be hugely controversial to have soldiers taking over from striking teachers, Col Kemp says.

If the internet was a sector, it would be the UK economy's fifth largest, bigger than healthcare, construction and education, according to the Boston Consulting Group.

Image caption Many parents take time off from their own jobs when teachers go on strike

IT and internet workers are absolutely essential to the economy, says Paul Zwillenberg, a partner at the consultancy. "The internet is becoming like electricity and like water - it touches all parts of the economy. If it were to stop it would impact every sector and have a major impact on growth."

A strike by all IT workers would be devastating for data centres, e-shopping, mobile phone services and banking. "It would make the Blackberry outage seem like a drop in the ocean. The internet would continue to function but it would be very hard for people to get access and it'd be very slow - like using the internet in 1996," Zwillenberg says.

Much of the impact of vital workers withdrawing their labour is down to timing:

In 1984, miners made the mistake of striking in March and at a time when stocks of coal were high

Tube drivers know any action will have a hugely disproportionate effect during the Olympics

And baggage handlers' value goes up at peak travel times such as Easter weekend

It's hard to find studies even attempting to ascertain the most essential workers.

If you were to ask five different think tanks to come up with the answer they'd approach it in five different ways, says the Work Foundation's Lee.

People tend to focus on high-profile frontline services when others such as care workers withdrawing their labour might have a terrible impact on society, Lee argues.

And what of tax inspectors? How would the country function if it couldn't collect taxes?