I spend most of my time drawing politicians, trying to work out what makes them distinctive. The eyes, the expression, their mood: it’s all about finding people’s peculiarities and accentuating them. When I started, I’d focus on the face. Everything else was an afterthought. It wasn’t until I came across a drawing by the Norwegian cartoonist Finn Graff – a cartoon of Helmut Kohl, I think – that I realised what I had been missing. How much you can tell from someone’s shoes.

I didn’t discover this, so much as rediscover it. When I was a teenager, I worked in a shoe shop in my home town of Arendal, Norway. I used to challenge myself to identify the right shoe for a customer the moment they walked in. It helped that they usually wore some already, of course, because people don’t tend to stray too far from previous choices. But I could usually tell from the outset what sort of person they were, and whether to focus my sell on comfort, style, quality or price. My challenge was to get the customer to buy the first shoe I suggested.

Middle-aged men who had worn their brogues to destruction were likely to hate the process of shoe shopping. Simply by pointing out that the most expensive, durable brands would be instantly as comfortable as their worn-out wrecks and probably save them from having to come back for a while, they would often leave with more than one pair. Norwegians like to say, ‘There is no such thing as bad weather, only bad clothes’, so I would preach about the wonder of Gore-Tex to anyone entering the shop in an all-weather jacket. Interesting laces could convince a reluctant teenager out of his trainers and into something more stylish, much to the appreciation of the parent in tow.

Since then, footwear has been one of the first things I look at when I meet new people. It always forms the basis of my initial impressions. But the power of footwear in art was made clear to me when I came across the Graff depiction of Kohl: how his shoes expressed more about his character than anything else in the drawing. They were beautifully rendered, not just black shapes at the bottom of the legs. That made me realise that a person’s posture, body shape or even shoes could be as much of an identifier as big ears or a long nose. I realised, too, how many of the greats whose work I admired had clearly come to the same conclusion. Gillray, Al Hirschfeld, Olaf Gulbransson… they all let the feet do the talking.

The most obvious example of footwear being essential is, of course, Theresa May. By her own design, her shoes are her most recognisable feature. She uses them very deliberately to express herself, to the extent that caricatures of her wearing boring shoes don’t actually look like her. Most cartoonists in this country have clocked this, but you often notice foreign cartoonists not paying much attention to her feet. Putting May in dull shoes is like drawing her with a beard. Incidentally, if you did draw her with a beard, but put her in her kitten-heel shoes, it would still look like her.

You will see a variety of different shoes on Spectator covers. With Donald Trump, I will make the shoes as small as his hands, so his feet look trotter-like, but also sharp and pointy. Putin wears jackboots or army boots whatever the occasion. A smooth, polished politician will have smooth, polished shoes, whereas a more shambolic one might have less shine and perhaps untied laces. They’re little details, barely noticeable, but they make a big difference to the caricature.

Whenever I draw Angela Merkel, she wears comfortable, no-nonsense shoes. For the cover in which May and Nicola Sturgeon were fighting over the Union, they both wore statement footwear. The battle is raging as much between their heels as their swords or faces. When I drew Emmanuel Macron as the emperor with no clothes, just after he came to power last year (top left), I put shoes on him because there is something mildly grotesque about being naked with shoes on. It makes you look more naked.

Meghan Markle (above, middle) is tricky to draw, as are a lot of actors and actresses. Partly because they’re often beautiful, and beauty can be hard to caricature, but also because it can be tricky to distinguish the person from the characters they’ve portrayed. With Meghan it was probably more a case of the former and it took more attempts to get her face right than anyone else I’ve ever tried to draw. So when I drew her joining the royal family, I made her legs the focus, because her face alone wouldn’t show what a new and different addition she was. Her distinctiveness is all in the legs and feet, in contrast to the formal poses of the rest of the family.

In the ‘Carry on Brexit’ cover, which showed Boris Johnson and Michael Gove tugging the red bus, the legs also do the work. Gove’s are twisting inwards, to show the lack of determination to keep Brexit moving. Boris’s are pulling hard but not getting anywhere. And their shoes? Clownish.