With the Annual Accounting Scheme, you complete one VAT return per year instead of each quarter.
The advantages of using the scheme are that...
You do have to be careful not to build up a large unexpected balancing payment, so you need to monitor your total VAT liability over the year. The annual accounting scheme is also not good for any business with regular repayments of VAT as it then takes over a year to get your money.
You can continue to use the scheme until your annual taxable turnover reaches £1,600,000. If the turnover surpasses this threshold within that VAT year, you must notify HMRC and exit the scheme.