The Big Question: Why does London Underground suffer so much industrial action?

Why are we asking this now?

Yesterday was a miserable day for London commuters. Today promises to be worse, and tomorrow worse still. Friday should be OK, but next week, what feels increasingly like "normal service" on the Tube will be resumed, with another three-day strike. And the frustration and delays that passengers experience will not be made any easier by their not really knowing what the strike is all about.

The union involved, the RMT, has no dispute with London Underground's management, nor with Transport for London, nor with London's Mayor, Ken Livingstone. Their beef concerns an invisible body of accountants who are winding up the affairs of a company that ran into financial trouble. To a lot of confused angry commuters, yesterday looked like a return to the bad old days when "wildcat" strikes seemed to happen just for the hell of it.

But why are there so many Tube strikes?

Disputes on the London Underground are a regular occurrence, and each one is about something different. There have been two others this year. There was one in February 2006, closely following one over New Year. There were strikes in 2004, 2001, and 1998. They are all connected with attempts to make the underground more efficient and less expensive to run.

What is the current dispute about?

It has its origins in an old and very public row between Gordon Brown and Ken Livingstone over the best way to modernise London's ancient Underground system. The then Chancellor insisted on introducing private contractors through Public Private Partnerships (PPPs), believing that this would avoid the problems of missed deadlines and escalating costs that had bedevilled so many previous public contracts.

Mr Livingstone vehemently opposed PPPs, but Brown got his way, and a private firm named Metronet won two 30-year contracts, worth £17bn, to maintain and upgrade two thirds of the Underground network – all except the Northern, Piccadilly and Jubilee lines. This year, Metronet came back asking for an extra £551m, undermining the whole point of PPPs, which are supposed to transfer the financial risk from the state to the private contractor.

On 16 July, the PPP Arbiter, Chris Bolt, told them that they could have an extra £121m. Two days later, the firm said that was not enough, and asked for the PPP contract to go into administration. When the administrators have done their job, it is expected that Transport for London will take over the contract – a belated victory for Livingstone in his old feud with Brown. Meanwhile, the three unions who represent staff employed by Metronet – the RMT, TSSA and Unite – have said that it is not their members' fault that the firm bailed out. They have demanded guarantees from the administrators that there will be no job losses, forced transfers or loss of pension rights. After long talks involving London Underground managers and Ken Livingstone, two unions say they have been given the assurances they wanted. But those assurances are not enough to satisfy the RMT.

Isn't the RMT quite left-wing?

Jimmy Knapp, the Scot who created the RMT by amalgamating the National Union of Railwaymen with the National Union of Seamen in 1990, was a traditional mainstream Labour Party stalwart. But the relationship between Labour and the RMT went sour after Knapp died and Bob Crow was elected RMT General Secretary in February 2002. In 2004 the RMT formally ended its affiliation to the Labour Party, breaking a link that dated back to 1899.

Crow was an old member of the Communist Party, who joined Arthur Scargill in setting up the Socialist Labour Party in 1996. Though he later let his membership lapse, he is still a socialist. He also supports Millwall. Millwall fans are known to chant, "No one likes us, we don't care", which seems to encapsulate Crow's message to London commuters. He once said: "I'm not one of those union officials who continually say they regret the inconvenience caused by industrial action. You cannot have a dispute without inconvenience to the travelling public."

Is this a 'wildcat' strike?

Maddening though it may be to be on the receiving end of it, the industrial action by 2,300 RMT members bears no resemblance to the sort of instant walk-outs that beset industries like car manufacturing a generation ago. Then, most workers were unionised. In fact, millions had no choice but to be union members, because of closed shop agreements.

Since the 1980s, the picture has changed radically. No one now needs to join a union if they do not want to. There is a strict procedure that must be followed before a union can call a strike, with heavy penalties for those who break them. If anyone thought that the RMT had broken the rules this week, they would be hauled in front of a High Court judge a lot faster than a Tube train moves on the Piccadilly line.

At the same time that union laws were made progressively stricter by the Conservatives, union membership went into chronic decline because of changing patterns of employment. However, the railway unions have been less affected than others by this decline, because of their strong traditions and the centralised nature of the industry. Though the RMT is a relatively small union, it is one of the few with the muscle to bring a section of industry to a standstill.

So is it all Bob Crow's fault?

Yesterday, Mr Crow's photograph appeared prominently on the front page of London's Evening Standard alongside the headline "Man Who Stopped London In Its Tracks" (not the first time the paper has singled him out in such a manner), so he is clearly in line to be the union boss we all love to hate. But there is strength to his claim that he is just representing his members.

Crow was convincingly elected and re-elected to his job. RMT membership has risen by a third under his stewardship, allowing it to claim to be Britain's fastest-growing union. Union militancy on the Underground has little to do with Mr Crow's politics, and a lot to do with the nature of the job. A Metronet maintenance worker works at night, deep underground in grim conditions on a network that has been allowed to deteriorate for too long, for wages of between £25,000 and £30,000 per annum. They used to be public-sector employees. Then the award of PPP contracts turned them, unwillingly, into private-sector employees.

Now they are neither one nor the other as they wait for the financial mess left by Metronet to be sorted out, with the lurking fear that sooner or later they will be made to pay for the company's losses. Their frustration is understandable. Almost as understandable as the exasperation of several million travellers stranded above ground.

So does the RMT union deserve the wrath of commuters?

Yes...

* The three unions have been given all the guarantees they asked for. Two are satisfied; one goes on strike

* On the London Underground, it seems, any excuse for a strike will do

* The RMT has a left- wing leader with a political agenda

No...

* It is not the maintenance workers' fault that their jobs and pensions are threatened.

* The union warned five weeks ago that trouble was brewing

* The root of the trouble is the decision to bring in a private consortium to do maintenance