People worry about things that might happen especially if it might effect them and it might happen.
Mights with a budget are a bit pointless It will be issued when they say it will. Sometimes it looks like there is a surplus - that can mean that there might be a tax reduction. We can more or less forget that one.
There is another aspect that is occurring in the US. Trump's income tax cuts. They were for a limited period that ends next year. Biden has let it be known that he intends to end it and change it to people who need it getting it so the more moneyed are looking at just what to do with it so that they still gain. Best keep quiet about budgets when that is possible. Biden sees his aim as good for votes.
Fuel duty here is similar. The freeze extends into 2025 so when that lapses there is an opportunity to change it. It looks like +5p puts it where it should be would gain them a couple of £b.
Interesting page illustrates the total effect of tax on fuel. Notice how it's falling as crude prices started reducing.
This chart tracks the changes in petrol and diesel prices over time (weekly on a Monday, rolling ten year period) and is based on BEIS data published each Tuesd
www.racfoundation.org
Try to find the take from fuel duty and vat on fuel. That was what I hoped to find but failed. I did find this which includes a dead link.