After the first couple of speeches, Sir Roger Gale - standing in for the Speaker - tells MPs how limited for time the debate is.
With proceedings having to wind up by 2.30pm, and speeches supposed to only last five minutes, some simple maths shows that just over 30 MPs will be able to speak.
Sir Roger says: "It's understandable that a lot of members would wish to take part on both sides of the House and in both sides of the argument.
"Looking around, it's quite clear we cannot accommodate everybody.
"That means that inevitably, it is likely that will be quite a considerable number of interventions.
"All I would say gently, is that interventions will be taken into account when considering the order of priority in which members are called."
This means that those who tend to get picked to speak towards the end of the debate - like Jim Shannon - may end up intervening more as they know they will not get called.