How does the Letwin Amendment work technically?

Question

On 25 March 2019, the UK House of Commons passed the Letwin Amendment, which stated, in part:

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Standing Order No. 14(1) (which provides that government business shall have precedence at every sitting save as provided in that order) shall not apply on Wednesday 27 March;

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(for full text, click here and search for "Amendment proposed: (a)")

There were a lot more details in there that I don't understand, but I got the point that parliamentary business would follow Letwin's plan on 27 March, and it did.

Now I'm given to understand that parliamentary business will follow Letwin's plan again on 1 April. How is this being accomplished technically, in terms of parliamentary rules? Nothing in the original amendment mentioned 1 April.

A comprehensive answer to this question would explain all of the following, but I'd be happy with answers that explain any of the following:

• How is parliament's business normally set, and what rules control it?
• What rules does the Letwin Amendment override, and what does it replace them with?
• Was there some motion passed mentioning 1 April? If not, how did it get selected as the next Letwin-guided date?
• Will there be more Letwin-guided dates after 1 April? Who will decide and how?

Answer 1

Normally, under Standing Order 14, proceedings of the House are set by the Leader of the House (Andrea Leadsom), with agreement from the Speaker. She will set out every Thursday the plans for the next week, with the precise motions being published on the Order Paper in the morning.

The motion on the 25th of March overrode Standing Order 14 and allowed the Commons to set the agenda for the 27th of March, through a Business of the House motion to be voted on after PMQs.

The said Business of the House motion set the precise procedure that was used on that day, as well as allowing the Commons to set the agenda for 1 April. (The full text of the motion is on the Order Paper).

On Monday, there will be another Business of the House motion expected around 5-6pm to set the precise procedure for that day.

EDIT: Sir Oliver's proposed Business of the House Motion for Monday has reportedly just been published (source), and if passed, it would result in a further repetition of this process on 3 April.