It is toe-curling when a politician's spouse is wheeled out to win votes

"Sorry Ed," tweeted the walking beer belly in dad jeans, "it seems I knocked your 'I'm a human' piece down the news agenda." Clarkson was referring to a publicity campaign on behalf of the Labour leader which included an extended interview with Mr Ed in The Guardian that uncovered his near obsession with Ronnie O'Sullivan, the snooker player, and a BBC News sit-down with the politician and his barrister wife, Justine Thornton.

Next week, we are promised, it will be the turn of Nicola Sturgeon. There is no word yet whether the First Minister's husband, Peter Murrell, chief executive of the Scottish National Party, will be taking on the Justine role. Given the couple's canniness, one suspects not. For there can be no spouse more on a hiding to nothing than the political other half out to do their bit. Like watching a seal balance a ball on its nose, or observing more than half a million people urging the BBC to spend even more of the licence fee on Jeremy Clarkson, one is filled with wonder not at how such things are done, but why.

Not that Ms Thornton was going to entertain such doubts, at least not on camera. Unlike several other political spouses, she has been backwards in coming forwards. This, indeed, was billed as her first major broadcast interview. The main point she wanted to get across was what a good, principled man her husband was, and how they knew there was hostility coming his way in the General Election campaign, but they would handle it. In the next couple of months, she said, things were going to get "really vicious, really personal", and that was without any walkabouts in Scotland. Viewers also saw the Miliband family in the park, acting natural, or as natural as one can be with a camera crew and reporter in tow.

It was all very 2015 media-friendly but it was also the stuff of which squirms are made. Looking at her, one wondered how comfortable she was with the move. One wondered even more when a newspaper carried a correction saying that references to Justine Thornton had been changed to Justine Miliband "to reflect Labour's statement that she wished to use the surname Miliband in political life".

In short, she wants to keep the professional and personal separate from the political - unless it suits her to do otherwise. Such is the minefield any politician's spouse enters into when they agree to play up and play the game in the interests of their partner, the party, and the payments on the new extension.

The first political spouse to stick her head above the parapet and receive pelters was Eve. Had it not been for the business with the apple, Adam could have been president of paradise forever. It is the mass media age, however, that has truly given rise to the phenomenon of the spouse as political player, with the American press in particular keen to lend a hand. On the part of politicians it was always about naked gain, as in 1952 when a certain senator called Richard Nixon, facing an expenses scandal, cited his wife Pat's lack of a mink coat and possession of a "respectable Republican cloth coat" as proof of his probity. Pause for laughter. But it was JFK and Jackie, the king and queen of Camelot, who did more than any other political couple to sell the idea that spouses could add to the package in attractive, vote-winning ways. No one was ever going to match that pair for glamour and guile, but that did not stop imitators, all of whose efforts turned to dust or terrible headlines. It only ever worked, worked in the sense that they got away with it, when the spouse was content to play a minor, largely non-speaking, firmly in the background, role. So Laura Bush thrived while Hillary Clinton was pilloried relentlessly.

UK politicians took longer to be seduced by the idea of using their spouses for political gain. Not for Mary Wilson the glossy photo-spread or the recipe sharing. Nor were Norma Major or Denis Thatcher keen to be interviewed, photographed or otherwise come within 10 miles of a journalist if they could help it. One had to wait until Tony and Cherie Blair to find a political duo with ambitions to be the next Jackie O and JFK. In their case, alas, they were more Crossroads than Camelot, the height of naffness rather than sophistication.

After Tony and Cherie things were meant to change. The new political generation wanted to do things differently. Spouses were now expected to have careers, and usually names, of their own. Miriam Gonzalez Durantez (wife to Nick Clegg) is a lawyer. Justine Thornton (or is it Miliband?) earns a crust from the law too, while Samantha Cameron is something in handbags. Yet for all their attempts to appear different, to not look like the little woman who has been wheeled on to make their husband seem human, there is not one of them who is not ultimately diminished by doing so. It is the same old sexist, toe-curlingly gruesome nonsense, wearing a different outfit. The only remarkable thing is why, in 2015, and given all that has gone before, they think the voters will play along.

Does it matter what a politician's other half does for a living or looks like? One would not judge the professional competence of a plumber or a doctor on the strength of whether their spouses were up to the mark. Programmers and teachers are not required to have their wives or husbands on hand to vouch for them. So why politicians? The electorate dismisses such interventions as meaningless stunts, the media has fun at the families' expense, and the opinion polls shift not a jot.

Times are changing again, though, and for that the credit must go in large part to Scotland, and female politicians in general. Sarah Brown and Moira Salmond showed the way to keep a private life just that. A new generation of women politicians, including Nicola Sturgeon, Natalie Bennett of the Greens and Leanne Wood of Plaid Cymru, have gone further, preferring to keep their partners out of the frame almost entirely; a pretty neat trick on Ms Sturgeon's part since her husband is a major political player. One can only hope, Scottish Tory leader Ruth Davidson's recent party election broadcast aside, that this is the way of things from now on. Just as dogs are not just for Christmas, so the partners of politicians are not just for photo ops.