My friend recently posted on the car seat UK page and they were rude as hell! Her daughter was escaping the straps and I even put her in myself and there was NO WAY the head rest would go lower/straps go tighter despite them banging on about it. They were so bloody rude. In the end she bought the Be Safe clip and it has kept her in her car seat now 🙂
I sort of had this problem with my daughter in her maxi cosi seat. She would somehow escape every time and I tried everything to stop it. I ended up moaning to the company even months after the warranty period I bought the seat from and they gave me a store credit for a different seat. I got a completely different seat and she hasn’t had this issue since. If not worth trying those be safe clips.
From what I’ve seen on the Facebook group “car seat safety U.K.” a child getting arms out is usually a fit issue. Meaning the headrest is too high or too low or the straps not being close enough to their neck when tightened. If you join the group you could just search for posts asking about getting arms out and see if the suggestions for them would help you. There is also one type of seat belt collector that’s recommended to use that could also be worth a try if seat adjusting doesn’t work. Xx