Andy McSmith: Reid was so conservative he made Cameron look like Robespierre

Sketch: Lord Reid's new best friend heard all of this with a frown of polite attention

"This time he's bringing his Dad" was the tagline for one of those Indiana Jones movies in which Dad was a grumpy old Scot played by Sean Connery. When David Cameron presented the case against reforming the voting system, he brought along a curmudgeonly Scot old enough to be his father. It was the former Labour home secretary, John Reid.

The Prime Minister read his speech briskly, like a man who needed to be somewhere else urgently. Lord Reid of Cardowan took a perambulating stroll in and around his text, savouring the pleasure of appearing alongside a Prime Minister for the first time in four years.

And how the audience loved him. Appreciative laughter and applause followed him through a discourse on constitutional reform that was so conservative that it made Cameron sound like Robespierre.

To change the electoral system to suit the Liberal Democrats would be "an outrage", Lord Reid declared. AV is "not fair, it's not equal, and it's not British!"

Lord Reid's new best friend heard all this with a fixed frown of polite attention. Mr Cameron was not making patriotic noises. He preferred a reasoned warning of the evils, as he saw them, of hung parliaments and coalitions that will become more likely under AV.

If politicians knew that a coalition was the likeliest outcome of every election, "they may start to put things in their manifestos that sound good but they can't deliver, because they know in a coalition they will not be made to answer for them," he said. How poor Nick Clegg's ears must have burned.

That name cropped up when a journalist asked Mr Cameron what he thought of the way the No campaign has used the Deputy Prime Minister as their bogey man. "I don't run the No campaign," he replied. "I certainly don't condone any personal attacks on anyone."

At which point Lord Reid raised another laugh by adding: "We're prepared to share platforms. I don't think the Yes campaign are" – which was not precisely a personal attack on Ed Miliband, who won't share a platform with Nick Clegg, but it was a dig.

It is fine to aspire to keep personalities out of a serious campaign, but they are what makes the contest interesting to the great majority who are not constitutional wonks. As David Cameron acknowledged, there are millions out there who are "not engaged" with the argument. Lord Reid added that he is worried about "a derisory turn out" on 5 May.

Meanwhile, the Tory MP Eleanor Laing was saying: "If hardly anybody votes in London and a very large number vote in Scotland and Wales... [the] result will be called into question." Cunning that. Even if the "Yes" campaign wins, some MPs will say that the turn-out was too patchy to make the result valid. It's the kind of escape against the odds that was Indiana Jones's speciality.