Prime Minister’s Questions (or PMQs) is soaked in lots of old traditions and conventions, and this is just one of them. By convention, the first question has to be about the PM’s engagements for the day, and then the questioner is allowed a ‘supplement’, which is, of course, the actual question s/he wanted to ask.
‘Number 1’ simply refers to the order number of the question on the daily parliamentary Order Paper, which summarises the parliamentary business for the day.
The engagements for the day question is pointless, since the answer is almost always the same: “This morning I had meetings with ministerial colleagues and others, and I have further such meetings later today”. You might think that something so pointless should be scrapped, and you’d be right. But British parliamentary conventions never had much to do with sense and reason.
If you watch PMQs for long enough, you will also realise that the entire exercise is pointless. The questions from the PM’s own team are just pre-planted opportunities to sing the government’s praises. Naturally, the opposition parties try to ask ‘difficult’ questions, but there’s no real point. If the question is vague and generalised, so is the answer. If the question refers to factual specifics, the PM can just say “Obviously, I don’t have the specific figures in front of me, so I can’t comment, however let me just repeat that our policies have been very successful… blah blah blah”.
Also, if awkward facts and figures arise, the PM is entitled to simply palm the question off to the relevant minister for a later reply (when they can work out at their leisure what the hell to say), usually using the all-purpose formula of “That is chiefly a matter for my Right Honourable Friend the Minister for [whatever department] to answer, and I will of course be happy to arrange for the Minister to address ths question in due course, but may I just point out that our policies have been very successful… blah blah blah”.
It’s just a charade. It’s only fun if the leader of the opposition is good at verbal knockabout stuff, and can try to stick lit matches under the PM’s toes, so to speak. The Thatcher years were rather dull in this respect, since the Opposition Leader at the time (Neil Kinnock) was crap at this part of the job, and Maggie ran rings round him with ease. It was a bit more fun when the Tories were led by William Hague. Hague was sensationally crap at all aspects of running the Tory party, with the singular exception that he was pretty good at the PMQ thing, and could rattle Blair’s cage quite well. Now we’ve got Iain Duncan Smith ‘leading’ the Tories, and he’s useless at PMQs, so Blair gets off lightly.