If your business is not making sales but you are still incurring costs, HMRC may refuse to repay the input VAT on purchases and ask you to cancel your VAT registration voluntarily as there are no business activities.
This is a drastic solution as you will lose your VAT number. If your trade picks up again later, you will have to reregister for VAT and be allocated a new VAT number. There may also be VAT liabilities to pay if you have reclaimed VAT on large building costs under the capital goods scheme.
As an alternative to deregistering altogether, you could keep your business within the VAT system and retain its VAT number by joining the VAT flat rate scheme (FRS). You cannot reclaim input VAT while you are within the FRS although there is an exception for VAT on purchases of capital goods which cost £2,000 or more.
A business can join the FRS at the beginning of the VAT period after submitting its FRS application unless HMRC agree an earlier date. You can leave the FRS on any day, even in the middle of a VAT period, so joining the FRS could be a temporary solution to your stagnant trade problem.