Analysis By Nick Assinder Political Correspondent, BBC News website

Before the fuel protests erupted, Gordon Brown's big speech to the TUC was going to be notable almost entirely for what it said, or hinted, about the current state of play in the Labour leadership.

Brown's comments

With some unions pressing the prime minister to step aside in favour of the chancellor sooner rather than later, Mr Brown's words were set to be picked apart for any indication of his own intentions or expectations.

Similarly, the audience reaction to his speech would have been analysed for any signs that the love affair between the union movement and the chancellor was finally cooling.

And there was plenty of opportunity for that with another of his classic "I'm your man" performances that once again set out his Labour credentials and attempted to remind the union movement why they still look to him.

Now, thanks to threatened fuel protests, tomorrow's headlines are more likely to concentrate on whether the chancellor can avoid a re-run of the 2000 petrol crisis, which threatened to bring the country to a standstill.

Concessions

But Mr Brown's reaction to the lobbyists' threats will still feed into the leadership equation.

Both Brown and Blair will seek to display their tough, "trust us to lead" faces

Five years ago the government response to the crisis was shaky and both the prime minister and the chancellor suffered as a result, with Mr Brown probably the greatest loser.

In the end, of course, he was forced to make concessions to the protesters. Things are likely to be very different this time around.

One lesson ministers took from the 2000 crisis was that early sympathy for the protesters started to wear off as soon as the public became inconvenienced by their actions.

This time the protesters cannot even claim the high fuel prices are a direct result of recently-increased taxes, suggesting public sympathy may be thin on the ground.

Warnings

So it is no surprise that the chancellor is not offering any concessions and that the government as a whole is planning a tough response to any disruption or blockades.

Contingency plans have been laid and warnings have been issued about breaking the law.

It seems both Downing Street and the Treasury believe tough action will go down best with the public.

As with Margaret Thatcher and the miners, Mr Blair and Mr Brown appear to believe facing down the protesters will ultimately strengthen their hand.

That is certainly the message that came through in the chancellor's TUC speech on Tuesday morning.

Stability

And, barring any major change in the mood - such as unexpectedly powerful support for the protesters from the public and motorists - that is likely to remain the case.

There are obvious risks to this approach, notably from the growing campaign for cuts in fuel tax over and above the recent freezes in the duty.

And if the protests escalate into a genuine national crisis there can be no certainty about how it will affect the government.

But, for the moment at least, there will be no softening of either the chancellor's or the government's line.

Both Brown and Blair will seek to display their tough, "trust us to lead" faces.

Meanwhile, for the third year running, Mr Brown used his TUC speech to demonstrate his Labour credentials and show that he is as much at home in this forum as Tony Blair is uncomfortable.

There was lots of talk about workers' rights, through the Warwick agreement hammered out between the government and the unions, full employment and continuing economic stability.

And, if the reaction is anything to go by, many in the Brighton conference centre can't wait for prime minister Brown.