Should your turnover fall below £83,000 in a 12 month period you may deregister your business for VAT. You are not obligated to do this, however, you can should you wish. Deregistering for VAT means you will no longer be able to claim back the VAT on the products and services purchased in the course of your business activities.
If you want to deregister you must contact HMRC directly and make them aware of your change in circumstances. Should HMRC have reason to believe your turnover will take you above the threshold, you will have to persuade them that your takings will reduce and will stay at this reduced level for a period of time.
There are certain instances where you must deregister for VAT. Should your business stop making taxable supplies, becomes part of a group, or if the business is sold the company must be VAT deregistered. Certain structural changes may also mean deregistration is mandatory. If you are in any doubt whether your business should be registered for VAT or not, consult the advice of an accountant for professional guidance.