Well, Tony: whose side are you on?

Fetch that man a reinforced handbag. Bring him a blonde helmet of spun steel. Get him stab-sharp stilettos. Tony Blair has often given the impression that he fancies himself as a centre-Left reincarnation of Margaret Thatcher. Such is his fascination with the old dreadnought that her name has featured in his utterances much more often than that of any other predecessor, Labour premiers included. He most recently invoked her example in an attempt to answer those wondering just how much his Government has really achieved. By the equivalent stage of her premiership, said Mr Blair, "the Thatcher government had still not passed its major trade union legislation ... or had the miners' strike".

The miners' strike? This struck me as a very odd event to be highlighted by a leader better known as a lover of consensus rather than a seeker of confrontation. Why reawaken memories of that searing episode - certainly for the Labour Party - of 20 years ago? It suggested a yearning within Tony Blair for a dragon to slaughter of an equivalent threat to Arthur Scargill's massed pickets.

The Prime Minister should be careful what he wishes for. A wave of trade union militancy - the like of which we have not seen since those pitched battles of the Eighties - is beginning to sweep Britain. The scenes are becoming resonant of the Jurassic period of British industrial relations: the picket lines, the employers using strike-busters, the union leaders responding by brandishing the cudgel of a full-blown, national dispute. Another sign that we are time-warping is the exhumation of deathly clich?s. Those nostalgic for the good old, bad old days will especially relish Bob Crow of the RMT, a man who rarely gets out a sentence which does not begin: "At the end of the day." In addition to the action which is causing so much disruption to the railways, staff in benefit offices have been walking out, postal workers are balloting for a strike and prison officers rumble menacingly. Where they lead, others may follow - especially if they succeed. It would be going too far to compare this to the titanic struggle between Margaret Thatcher and the miners. Where that was a battle of the trenches, these strikes are more akin to guerrilla warfare. In many ways, this actually makes them much more difficult for the Government to handle.

When Tony Blair was elected in 1997 he made it clear that he would be doing no favours for the unions. And it is precisely because many unions feel the Government hasn't done them any favours that they are shifting to the Left. While the RMT threatens to terminate its sponsorship of Labour MPs, the GMB is slashing contributions to party funds.

Reasonably or not, unions expected a Labour Government, even a New Labour Government, to be the workers' friend against the boss class. They have been largely disappointed. True, Mr Blair has introduced the minimum wage and made it easier for unions to win bargaining rights with employers, but neither is regarded gratefully by rail or postal workers who earn well above the minimum and whose workplaces were already heavily unionised. Even John Monks, the mildly mannered and impeccably moderate leader of the TUC, is sometimes driven to spit with frustration about the Government.

These strikes are the jagged edge of a wider discontent which is being turned into aggressive action by a militant new breed of union leaders who are rather more savvy than Mr Scargill. Where he led miners and their families into terrible poverty and abject defeat, the RMT has so far deployed much more cunning tactics. The use of 48-hour strikes maximises the grief to passengers while minimising the impact on the strikers' pockets.

It is surely not coincidental that these strikes are intensifying in the run-up to the RMT's leadership election in which Mr Crow will hope to triumph by demonstrating that his methods get results.

If he wins that election, it will continue a trend. The Blairite-preferred moderate was trounced by Mark Serwotka, a supporter of the Socialist Alliance, for the leadership of the Public and Commercial Services Union, the largest in the civil service. The fire brigade union - another one to bring on nightmare memories of the Winter of Discontent at Number 10 - has elected a more aggressive leadership. The appropriately named Andy Darken, the militant new leader of the Prison Officers' Association, is already darkening the thoughts of troubled ministers about the mayhem he could stir up. A symptom of the anxiety this is causing within the Cabinet is that the Government is tiptoeing away from some of its proposed reforms to the police. When militancy is contagious, the last thing any Government needs is an unco-operative police force. David Blunkett is retreating from plans to reduce their lucrative overtime pay. What an exquisite irony we have here. Union action led by the hard Left will put more money in the pockets of the police, crushers of the miners.

It is the strikes on the railways that pose the most immediate challenge to the Government. Should the RMT score a victory, then other unions will be encouraged to match their belligerency. If there is no settlement, it is not hard to forecast the consequences of a protracted and increasingly ugly dispute. Commuters will suffer, as will the businesses they work for. The rail companies will lose money, jeopardising investment and demanding yet more subsidy from the taxpayer. And the Government will get what it is most keen to avoid: the blame.

Secret ministerial attempts at mediation have proved fruitless. Exhortations to settle this strike by arbitration have gone unheeded. If the rail network is paralysed - even more so, if postal services are also crippled and the prison officers strike - ministers will not win respect by wringing their hands. At the end of the day - I'm afraid it is infectious - the Government will be compelled to take sides.

Then we may see exactly how far Tony Blair desires to pursue parallels with Margaret Thatcher. When he muses about confronting mass strike action, the Prime Minister should be careful what he wishes for - lest his wish come true.

? Andrew Rawnsley is chief political commentator of The Observer.