VAT

It’s not necessary to register for VAT unless your business hits the VAT turnover threshold. At the time of writing, that’s £85,000.

A couple of things to note:

1. The threshold is based on turnover not profit
2. You don’t need to be a limited company: sole traders can register, too
   
3. You shouldn’t charge VAT on services unless you’re VAT-registered
   

You can choose to register voluntarily if your turnover is below this limit. There are situations where this may be useful, but it’s certainly a topic to cover with your accountant.

There are more details about registration on the GOV.UK website.