The Speaker will call one of the MPs who tabled the substantive motion to move it and make a speech. In the case of a debate on a substantive motion in Government time, this will always be a minister.
The Speaker then proposes the question. At that point, the debate begins.
The Speaker will usually call a frontbencher from the official Opposition, a backbencher from the Government side, and a frontbencher from the third largest party to make speeches early in the debate.
The Speaker will call any other MPs who want to speak to the motion, including any MPs who’ve tabled amendments to it that the Speaker has selected. If you’ve tabled an amendment that’s been selected, you should start your speech by saying, “I beg to move the amendment in my name on the Order Paper.”
There’s no fixed time limit for speeches, but the Speaker may set one if lots of MPs want to speak.
During the last half-hour or so, the Speaker will usually call another a second spokesperson from the official Opposition, followed by the minister to sum up the debate.
If there’s a Business of the House motion relating to the debate, this will usually set out how the debate will be brought to an end. It can allow for the Speaker to put the questions on any amendment(s) and the main motion after a certain period or at a certain time. There may be votes.
If there’s no Business of the House motion, the debate will often finish just before the moment of interruption, to enable MPs to take a decision on any amendment that’s been moved and the main motion. There may be votes. If there’s no Business of the House motion, and the debate is still underway at the moment of interruption, it is interrupted. This means MPs can’t decide on any amendment(s) or the main motion.