Supply and Appropriation Bills give authority for the Government to use the expenditure requested in the estimates and to be issued with money from the Consolidated Fund (the Government’s bank account). In addition, they also place limits on the purpose for which the money may be spent by setting out the services particular budgets are to be used for.
A Supply and Appropriation Bill includes a schedule containing the substantive content of the estimates that have been approved by the House.
There are two of these bills each year: one for the supplementary estimates and votes on account and one for the main estimates.
A Supply and Appropriation Bill will normally receive its first reading immediately after the estimates motions have been agreed on an estimates day. As with other bills, first reading is purely formal and doesn’t involve debate. Second reading then takes place the following day but the question on second reading is also put formally, without debate. The bill doesn’t have a committee stage, but instead proceeds straight to third reading, which again takes place formally, without debate.
The House of Lords, which has no role in the estimates process, passes Supply and Appropriation Bills without debate.
You can see an example of a Supply and Appropriation Bill.