The VAT regulations are never to be underestimated. They are complex and the powers of the Customs side of HMRC are draconian. HMRC will ask you to pay VAT monthly if your quarterly VAT payments exceed the threshold for quarterly payments.
There may be other circumstances as well, but there is no room for appeal, unless the quarterly VAT payment giving rise to a breach of the threshold is a one-off and you can demonstrate that this happens infrequently.
To find out more, call us on +44(0)330 024 3200, and talk to one of our VAT experts.