1st registration for tax return

Hi, I've just spoken to a self-assessment tax advisor on the phone this morning, I have registered and awaiting my UTR in post (according to the website), do I have to wait for this code before I can complete my tax return ? I am going around in circles on the internet and the advisor told me I could complete all of today online Thanks 

Name removed admin .

Hi Anne,
Once you have your UTR you can then enrol to file your Self Assessment online. When you register you are sent an activation code in the post to activate your Self Assessment online account. You will need to wait for the activation code before you can file the tax return online. 
Thank you.