Is this the winter of Ken's discontent with Tube unions?

But yesterday life was back to normal, with a dispute over "safety" paralysing large sections of the system.

The Circle and Hammersmith and City lines were closed, along with part of the District line. Already this month we have had a full-blown Tube strike with several other disputes bubbling beneath the surface.

It is very confusing for passengers. Yesterday, the 35-year-old trains on the three sub-surface lines were deemed too dangerous for drivers to take out. Today, those same trains, with no modifications, are said to be safe. All it took was a quick onceover by London Underground inspectors.

No wonder passengers are bemused. Drivers from Aslef refused to operate the vehicles because of a reported problem involving the "deadman's handle", the device which stops the train should the operator collapse; RMT members followed them into dispute. The row has its origins in the deteriorating industrial relations in LU, heightened by the fallout from the collapse of the Metronet contract.

There was a legitimate safety concern, albeit a minute one. A driver found that the handle could be reset without coming to a halt. It was, therefore, theoretically possible for a driver to collapse over the handle and for the train to start accelerating again. However, that risk was very small. In an organisation with good industrial relations, such concerns would be raised through the appropriate channels and dealt with quickly.

This is not the case in LU, where industrial relations have, since time immemorial, been lousy. The workers are all too ready, as one exasperated manager put it, to "walk before they talk". This was a wildcat strike rather than a safety dispute.

Similarly, the dispute earlier this month over the Metronet collapse was equally arcane. Bob Crow and the RMT sought assurances from the Transport for London management over job security and pensions following their transfer when the Metronet issue is resolved. A management letter was deemed unsatisfactory and we had two days of dispute, resolved, bizarrely, when another letter was written that almost paraphrased the first. The way that these disputes f lare up demonstrates the volatility of the unions. They remain riven by Left-wing factions often at odds with each other. The members, for their part, have seen that militancy has largely worked. They are getting above-inflation pay rises and the perception, if not entirely the reality, is that the unions have won several disputes simply by threatening to strike.

The rail unions are almost the last bastions of worker militancy, far less affected by the Thatcher battle than most because of their strong position. Oddly, they have done well out of privatisation, too. Some Virgin Train drivers operating out of Euston can earn £80,000 per year including overtime. But in London, with the election of Ken Livingstone, they have faced an enemy they do not quite know how to handle. Livingstone, in fact, has been surprisingly steadfast, standing up to the unions far more than might be possible for someone without his Left-wing credentials.

The renewed union militancy may be a risky attempt by some factions to get rid of Livingstone through the ballot box and replace him with Boris Johnson who they see, probably wrongly, as a patsy. Livingstone may be facing his own winter of discontent, and that could damage his electoral chances. The unions are angry that Livingstone wants to follow the three-year deal with one taking us past 2012. His aim is to ensure that the unions do not disrupt the Olympics.

Unfortunately, events this month show that even when industrial peace has supposedly broken out, there is always the potential for disputes. Until union members decide to stop voting for militant leaders, Londoners will continue to be at risk of unnecessary disputes on the Underground. They may even find themselves a pawn in their leaders' attempt to oust a man they see as having betrayed their cause.

Christian Wolmar's new book on the history of the railways, Fire and Steam , is published by Atlantic Books, £19.99.