The Government should revert to one major fiscal event each year, leading industry figures have said, while also calling for major reform of the tax system.
The Institute for Government (IFG), Institute for Fiscal Studies (IFS) and Chartered Institute of Taxation (CIOT) have written to Philip Hammond listing immediate changes they believe will improve and simplify the UK's tax system.
This includes stopping Autumn Statements morphing into second Budget announcements, which the groups say leads to "a proliferation of measures and very long finance bills".
They have written to the Chancellor listing recommendations for immediate reform, ahead of Mr Hammond's speech to the Conservative Party conference on Monday.
Jill Rutter, programme director at the IFG, said: "When she launched her leadership campaign, Theresa May said it was time to talk about tax. We agree.
"And the first thing we need to discuss is how to reform the Budget process to make tax policy fit for post-Brexit Britain.
"That means clearer direction, fewer surprises, a radical reduction in the number of measures and a willingness to engage the public on the big choices."
Paul Johnson, director of the IFS, said: "Nearly £4 in every £10 earned in the economy is taken in tax.
"How the tax system works matters enormously to us all. The current system for tax policy making is not fit for purpose.
"Too many changes are sprung on the country in too many fiscal events with too little sense of direction, consultation or evaluation."
The open letter reflects initial findings from a project being carried out by the IFG, IFS and CIOT looking at how to improve budgets and tax.
A full report will be published later in the year.