Gordon Brown faces a battle to regain his authority after bowing to pressure from Labour rebels in the row over the abolition of the 10p tax rate and unstitching the Budget to offer help to pensioners and young workers.

Mr Brown’s climbdown on Wednesday left him exposed to Conservative ridicule and emboldened some Labour MPs to claim they could now force him to retreat on plans to extend to 42 days the maximum period of detention without charge of terrorist suspects.