They have many names – I’ve yet to here one used consistently in any area of tailoring. But the side fastener, side strap, side tab, side buckle or strap and buckle, whichever name you use, creates an amazing sense of freedom once you have them on your trousers.

Two strips of cloth loop through either side of an old-fashioned buckle. The cloth is usually, but not always, the same as that of the trousers: right now I’m wearing some khakis with straps striped blue-and-white; it is a way to add a little character to casual trousers.

The cloth at the front is fixed, while that at the back is longer and loose. By pulling backwards on it the length of waistband under the side strap is pulled together, concertinaing and tightening the trousers upon the waist. The teeth of the buckle, which only run in one direction, prevent the cloth from slipping back. The only exception I have ever found to this arrangement is on Kiton’s new CiPa 1960 range, where the loose strap faces forwards. While this may have been popular on Italian suits in the sixties, it is far harder to tighten and an inferior system.

One thing that is also different about the CiPa side strap is that the rear section, attached to the trousers, is extended and widens as it goes across the seat of the trousers. It forms something more like a teardrop shape – and Kiton is not the only company to do this. One bespoke suit I have made by Cheshire bespoke in north England has straps designed in a similar way. My tailor refers to them as gun holsters.

Some tailors also have slightly differentiated straps: those I have on these casual trousers (from Segun Adelaja) are short and squared off; my bespoke suits from Graham Browne have longer, though still simple straps; Anderson & Sheppard straps are slightly lower on the waistband.

Indeed, when the trousers sit on the natural waist rather than the hips there is often a need for the strap to be slightly lower, across the seam connecting the waistband to the trousers rather than on the band itself, in order to give the top of the trousers more flexibility. As regards length, I find a shorter strap is better as it reduces the bunching to a concentrated area.

So that’s what they are. Why do they give you freedom? Well, for any man that cares about how his trousers fit, it is incredibly frustrating when you lose or gain a little bit of weight and suddenly your trousers don’t sit quite right. Your shirt becomes loose, your pleats collapse a little and most importantly, your trousers change length. Suddenly there’s a break at the back when you never intended one.

With side straps, that doesn’t happen. Little adjustments can cope with temporary adjustments in weight – many tailors will make trousers with side straps that tiny bit big, so you can adjust the waist out as well as in. And if any change in weight is permanent, the side straps ensure that your trousers continue to sit right until you can have them altered.

They are not a long-term solution – the cloth around your side seams will bunch together if the straps are too far tightened – but they’re a lot better than the alternative, which is elastic in the back of the waistband, fastened at the side on two or three button options. Elastic makes the wool wrinkle when tightened.

Go try a pair.