Yes, simply stating "I am not VAT registered" on invoices is sufficient.

You don’t need to be an LTD company to register for VAT, but under the Flat Rate Scheme (FRS), you pay a fixed percentage (e.g., 11.5% for IT consultants) instead of reclaiming input VAT.

You can register for VAT immediately after registering as self-employed. VAT registration typically takes 10-30 days, and HMRC will provide your VAT number once approved.

Under the Flat Rate Scheme, you charge clients 15% VAT but pay HMRC the lower flat rate percentage applicable to your industry. For further vat calculation you can visit here