The problem for the government is twofold. First, rising petrol prices are something which millions of people will understand and feel, so much more so than abstract talk about cuts, deficits and the like. And, second, it focuses attention on Alistair Darling's Budget next week. It won't be that surprising if he delays next month's planned rise in fuel duty, to try and defuse this issue politically. But even that will encourage more questions about the government's deficit reduction plan, and about whether they have made up the fiscal shortfall elsewhere. In the end, it's pretty much a lose-lose situation for Brown & Co.
P.S. If you need a reminder of how Gordon Brown can struggle in the face of rising petrol prices, then it's worth going back to his 2008 interview with Fern Britton, from around the one-minute mark: