An Imprest Supply Bill is Parliament's way of saying to the government 'yes you can have that money, but also if you find you need to use more money on it, you don't need to come back and ask again'.
A government cannot just spend any money it wants. It must have the approval of Parliament to open the till. It's the same for any extra government expenditure that becomes necessary down the line when unexpected things occur, as they usually do.
That's why this week in parliament, MPs find themselves debating not just the remaining stages of the Appropriation (2022/23 Supplementary Estimates) Bill, but also all stages of the first Imprest Supply Bill relating to the 2023/24 year.
That may sound a bit arid, but it is important, so we sat down with the Shadow Leader of the House, the National Party's Michael Woodhouse, to get his take on this process.
"We're basically forward-loading the government's ability to manage unexpected things into next year," Woodhouse explained.
"The main purpose of the Imprest Supply Bill is to give the Government authorisation to spend money in advance of the budget being passed into law."
The Appropriations (Supplementary Estimates) Bill is a sort of sequel to the recently delivered budget and contains end of year appropriations from the financial year about to finish. Normally at this point the second (or third if there is one) imprest supply authority expires, and so the next year's first Imprest Supply Bill is adjoined on to the debate on the supplementary estimates.
So before the financial year begins on 1 July, a first Imprest Supply Bill is passed. This legislation nominates an amount of money (more than needed) that the government has permission to spend until the government's annual budget, or Appropriation (Estimates) is approved.
It's Parliament's way of granting approval to government for use of funds to keep the machinery of state running, by saying 'yes you can have that money, but also if you find you need to use more money on it, you don't need to come back and ask again'.
Later, when the Estimates are approved, the first Imprest Supply Bill becomes useless and the authority it granted the government for spending expires. There are usually two or three Imprest Supply Bills each financial year, depending on the need for more interim appropriation.