By Ben Wright
BBC News political correspondent
Mr Brown is dealing with Labour opponents on several fronts
Rebellion. It's the word of the moment in Westminster.
In this world of tightly whipped discipline, any deviation from the party line is seen as a courageous act of career-crushing defiance.
But rebels are everywhere right now. Well, actually, they are everywhere in the Labour Party.
The rebels do not want to overthrow the government but they do want to change its policies.
Their great recent triumph was the 10 pence tax U-turn and their pin-up is Frank Field, the Labour MP who showed what could be done with a good argument and a clever campaign.
And now the rebels have organised on other issues: the government's plan to increase vehicle excise duty (retrospectively) on the most polluting cars; its proposals to reform the planning system; and of course its plans to increase detention without charge for terror suspects up to 42 days.
And, they reason, if the government is in the mood to appease bolshie backbenchers on the issue of 10p tax, why not these?
When Gordon Brown's working majority is 66 and poll ratings are plunging, he cannot afford damaging defeats in the Commons.
This coming week had pile-up potential, with one controversial policy shunting into the next.
Monday promised a key vote on the Planning Bill - a dull-sounding piece of legislation but with big significance.
Many Labour MPs are angry about what they see as a lack of political accountability in the government's plans for a new planning system.
But last week the bill was suddenly pulled from the parliamentary schedule.
One of the potential rebels, John Grogan, said: "Either the government doesn't want two controversial votes in one week or it's preparing concessions to meet backbench concerns. It's got to be one or the other."
Would-be rebels tend to reveal their identities by signing Early Day Motions, in-house parliamentary petitions that do not have any power to change policy but do reveal what MPs are getting cross about.
Ronnie Campbell started one asking the government to reconsider its vehicle excise duty policy and 53 MPs have signed it.
Mr Campbell has got a meeting with the chancellor next week to talk though his concerns. It is a rebellion the government is anxious to stall.
But the proposal that is really getting rebel watchers excited is contained in the Counter-Terrorism Bill.
The House of Commons votes on Wednesday on extending 28-day detention limit to 42 days - and the result remains impossible to call
A flurry of new amendments that beef up the safeguards and stress the exceptional circumstances in which the power could be used has won over some Labour MPs such as Keith Vaz and Martin Salter.
But an unknown number of others remain opposed to the central principle of the plan.
Of course, some of Labour's disgruntled MP are serial rebels, left-wingers who habitually vote against the government.
For others this is a bigger line to cross, particularly on a vote that - though not a confidence issue - carries the tag of being a major test of Gordon Brown's authority.
A rebellion is one thing. A rebellion that could dangerously wound an embattled prime minister is quite another.