I have received an Assos item in the post and it has what looks like a security tag still attached. It is a grey round cone shaped thingy.

Big magnet!

Just run when the security card clocks you, like the rest of us.

Take it to a local small clothing store with your proof of purchase to prove your genuine and offer them a small offering either to them or their charity box on the counter add a thank you. Or just mail it back to them.

What does the shop use to remove these then?

Seriously, I would contact Assos. You could risk damaging the shorts removing the tag.

A big magnet – usually built into the till.

Any Posties near you? I hear they are quite adept at removing tags from clothing.

You can cut the pin with a decent set of cable cutters.

Contact the shop where you bought them, perhaps?

As above, strong magnet

if it’s the type with the round bubble part on top, just cut the top off & you can release the security pin from inside, or so I was told once, ‘onest guv