Does starting VAT charges later affect liability for UK online stores?

[Markssxx]

I won’t be liable for VAT as my store turnover will be well under the threshold. I wondered if other U.K. based stores charge VAT at the start or later when they are liable to. Also if I don’t charge VAT from the beginning and my turnover exceeds the limit will I be liable for VAT previously. I will only be selling to U.K. customers. Appreciate any help.