Susie Rushton: Choose your best man with care

I wonder if, in the final analysis, when the whole story of Liam Fox and his friend Adam Werritty is unspooled, we will conclude that the Defence Secretary didn't only choose the wrong adviser. He chose the wrong best man at his wedding.

However many mates you have, it's not easy to select from one's social circle a friend who is hilariously funny and party-loving, yet just responsible enough not to lose the rings, screw up the stag do and make an idiot of himself and the groom on the day of the wedding.

That's why so many men now sit on the fence and split the job between two friends instead. The role brings with it plenty of scope for disaster and unfortunately Hugh Grant's hapless best man in the opening scenes of Four Weddings and a Funeral – having overslept, he arrives late for the wedding, without rings – isn't so far removed from reality.

My favourite piece of advice on choosing a best man is posted on the wedding website confetti.co.uk, which counsels: "avoid asking someone who is too busy, unreliable, notoriously difficult, or who has had a previous romantic relationship with the bride."

But the other, less obvious, quality needed for a best man is a kind of equality with the groom. Groom and best man isn't the same power dynamic as father and son, or teacher and student. So, to the casual observer, a powerful groom and a younger best man in thrall to the former makes a slightly strange arrangement.

Getting the balance of power right is why famous grooms so often choose a close relative as a best man – a brother or cousin is one of the few people who treats them equally. On Sunday, Paul McCartney married for the third time, with his brother Mike as best man. (Mike's a safe bet: he was chosen for the Beatle's previous two marriages, too.) In April, Prince William did the same thing when he picked Prince Harry – trust in a relative presumably winning out over any hope of a tasteful after-dinner speech.

By the time of Liam Fox's wedding to fellow doctor Jesme Baird in 2005, he and Werritty had known each other for about five years, having met when the younger man was studying in Edinburgh. At the wedding, Werritty dutifully made a speech that gently ribbed the groom.

Fox and Werritty look very smart, and very happy, in the photographs that have been reprinted across the media this weekend. So, on the face of it, Werritty did his best-man duties well. But the age difference – and the imbalance of power that suggests – is noticeable, and unconventional.

Did Fox regard his younger friend as a livelier, wittier version of himself, somebody who could charm and engage his guests – and later, his professional contacts at home and abroad? There's a lingering unspoken bond between men who agree to take up best-man duties for each other – so did Werritty's status as Fox's "closest friend" somehow trump all other considerations that the politician might have had? With consequences he would come to regret?