Rebecca Tyrrel: 'Margaret Rutherford cared about the ishoos'

Who knew that Tony Benn is a first cousin of the late lamented Margaret Rutherford? Admittedly their cousinhood was once removed, but this seems strangely fitting because some used to believe that Benn was once removed from reality. According to Kelvin McKenzie's Sun, he was the barmiest man in England. It was a title that, tragically, could have been applied to Rutherford's father, who bludgeoned his own father to death with a chamber pot – Agatha Christie would have certainly approved of the method. And Rutherford was quite an eccentric herself, of course. She built her film career playing up the battiness, happily without murdering anybody.

The more one reflects on the Benn/Rutherford blood tie, in fact, the more obvious it seems. Benn famously disowned a title (Viscount Stansgate) while Rutherford equalised the honours score for the family by picking one up. She became Dame Margaret, and rightly so. Like Tony, she cared about the ishoos. How else could she have taken on the country's least desirable post of St Trinian's headmistress?

Superficially, the physical resemblance was hard to discern. Dame Margaret was short and, latterly, almost perfectly square where Tony is tall and shaped like a pencil. She did not smoke a pipe, though she had a ruminative, philosophical quality which meant that it was never hard to imagine her – particularly in Miss Marple mode – puffing away off-set on a small cheroot.

One thing they unquestionably have in common is an engagingly mad, beatific gleam to the eye; both are unexpectedly warlike. Indeed, you might struggle to identify which of them said: "If the Germans had arrived, I tell you, I could use a bayonet, a rifle, a revolver, and if I'd seen a German officer having a meal I'd have tossed a grenade through the window". In fact it was Benn, likening Dad's Army to Iraqi insurgents, while Rutherford came out with: "If you imagine that I'm going to sit back and let everyone regard me as a dotty old maid, you're very much mistaken." But the quotes are interchangeable, and so is the enduring affection in which these timeless eccentrics – both loved for their kindness by those who knew them – are held.