Starting a contract before the VAT registration is complete.

[Craig@Clarity]

I usually advise on both options being available but in reality, I've found that the majority will invoice less the 20% and then issue a VAT only invoice. Either way, both routes are acceptable and achieve the same result and require the same admin. If you're lucky, the VAT registration will come in on time and this dilemma will go away

[chopper]

Or...

Wait until after your VAT certificate arrives before sending the first invoice. There isn't going to be a particularly long gap between contract starting, VAT registration number being issued and you needing to issue the first invoice.

[taxevo]

If you are six weeks away from issuing your first invoice then there is plenty of time for the certificate to come through. In the worst case scenario of the registration not being confirmed then issue an invoice without the VAT and you can easily issue a VAT only invoice once the details are confirmed. Just make sure you keep the agency/client up to date with what you plan to do.