A fourteen minute recording is available on the parliamentary website about the history and traditions of the Budget - http://www.parliament.uk/about/podcasts/budget.cfm. A factsheet is available at http://www.parliament.uk/documents/upload/p05.pdf.
The Hansard Society have done a lot of work on the current process - and proposals for reform. Their book, 'The Fiscal Maze' is downloadable at http://www.hansardsociety.org.uk/blogs/downloads/archive/2007/09/17/the-fiscal-maze-jul-2006.aspxBudget resolutions are passed to give effect to any tax changes announced - and these are then permanent effect after the Finance Bill is passed.
The Treasury maintains a Budget website at http://www.hm-treasury.gov.uk/bud_bud09_index.htm