Accounts Certification Threshold

Hi, just wanting to make sure I am remembering this correctly. I'm a full MAAT licenced accountant but I mostly handle small businesses (i.e. maybe £300k turnover maximum!). A customer has taken on a new contract which has significantly increased his turnover and I expect him to hit the million pound limit before his trading year ends. I am certain that this would mean he'd need to use a chartered accountant but I can't remember for definite and just wondered if anyone else could! Thanks!