Flat Rate Scheme turnover exceeded

I'm a bit confused about when a trader has to leave the VAT Flat Rate Scheme.

The turnover at the year end was under £230k (just), which was to 31 Jan 2012. However, on a rolling basis they will be over in the next month or so.

Do they have to leave the scheme when they exceed the turnover on a 12month rolling basis or can they wait until after 31 Jan 2013.

It seems to be on reading Notice 733 they can wait for another year end to pass but it doesn't feel right.

Assume for the purposes of this that their anniversary of joining the scheme is the same as their year end..

Many thanks.