Ignore the trousers for now. Yes, that’s right, ignore the shiny, zippered, ketchup-red trousers. They are only here to make a point about the trenchcoat. A trenchcoat is a timeless classic. Everyone knows that. It is perennially chic, it takes you anywhere, it is age-appropriate. It is eminently sustainable: buy one and it will last you decades.

This is all marvellous and sound and useful. But just because the trenchcoat is a practical, dependable, sensible piece to own, it doesn’t mean it has to be practical and dependable and sensible all the time. It is allowed to have a bit of fun now and again. It doesn’t always have to be in the mood for a white shirt and straight-leg jeans, or a pencil skirt and a fine-knit sweater. It can be in the mood for, say, shiny, squeaky, zippered, ketchup-red trousers.

Also, maybe this is just me, but I find making a trenchcoat look chic and neat is actually really hard. Looking good in a trenchcoat has long been about keeping the silhouette just-so. Reader, I lost a good week of my life in the early part of this decade trying to figure out how to tie the belt of a trenchcoat in an attractive-looking knot. If I fastened it tight, it was ugly; if I left it loose, it was messy. I stood perplexed in front of a full-length mirror, trying to work out why it was that the belt on my trenchcoat looked less elegantly nonchalant Jane Birkin and more like a six-year-old’s shoelaces.

And then there were the sleeves. A trenchcoat sleeve looks alluringly French pushed up to the elbow to show bare wrists and forearms. I see this all the time in photos. But if I push a coat sleeve up to my elbow, I can’t move my arms. (Maybe there’s something wrong with my arms? Although they seem to function quite normally.) Anyway. A trenchcoat sleeve also looks alluringly French if set off by a dazzling white shirt sleeve peeking out just-so at the cuff. In photos, that is. On me, a statement cuff looks less like a chic Parisienne off for a Left Bank coffee and more like a tantrum-prone 18th-century boy-prince about to tuck into a roast swan.

So let the trenchcoat loosen up. Wear it loose and rogueish, as if it was a cape or a dressing gown. Here. I’m wearing it with a velvet T-shirt from the back of my wardrobe, and with ketchup trousers – to make a point, as discussed. Because a trenchcoat is even more useful if it doesn’t always have to be sensible.

• Jess wears trench, £250, arket.com. T-shirt, Jess’s own. Trousers, £55, weekday.com. Boots, £99, office.co.uk. Styling: Melanie Wilkinson. Hair and makeup: Samantha Cooper at Carol Hayes Management.