I dunno if some people realise just how painful a poorly fitted helmet can be.. before I found one that fitted (it only took 15 years..), I used to swear that if helmets ever became compulsory, I'd rather stop riding bikes.
The helmets grip the head like a vice at the front and back, leaving indentations, yet they have massive empty gaps at the sides, which can't do much for the protection factor. On some of them, the adjustment straps dig into the lumpy area at the bottom of the back of the skull like a knife. It's not just a mild headache caused by wearing one for a bit - the pain is immediate, and it's torture.
All of the helmets sold by Decathlon are of this type, and I've been to quite a few bike shops where all their helmets are also like this. I'm not sure what Halfords are like these days - they used to be one of the culprits. I hope raleighrider21 has some luck with them!
I do wonder how many people have had the same experience as me, and either put up with the pain or don't wear a helmet. I can't be the only one with a weird head!