If you breach the mandatory VAT registration threshold in a given month, your Effective VAT Registration Date will be the first day of the second month following the month of the breach.
This means that if your rolling 12-month taxable turnover breaches the £85,000 threshold on 14 August 2022, your Effective VAT Registration Date will be 1 October 2022.
If you have temporarily exceeded the threshold and you think you are going to breach the threshold in future, then you may be entitled to claim a temporary exemption.