VAT flat rate scheme, when to leave the scheme?

Hi all,

I just wanted to double check my understanding of when a company should leave the flat rate scheme. I understand that it is when the turnover (including VAT) exceeds £230,000 in 12 months. My query is with regards to the period that counts as 12 months.

I believe that it was at any 12 month period from joining the scheme, i.e. on a rolling basis. However a colleague said they thought it was only at each anniversary of joining the flat rate scheme that you look back over the past 12 months.

Which is correct?

Thank you in advance for your help.