submit paper forms without UTR no.

I am stilling waiting for the UTR no. Can I mail paper forms without UTR no. to avoid late penalty? If in between, I receive the UTR no., I submit online again, will it be duplicated?

Hi,
You'll automatically be sent a Unique Taxpayer Reference (UTR) when you:

• Register for Self Assessment
• Set up a limited company
• Register a partnership

If you've already registered for Self Assessment you can find out when you should receive your UTR:
Check when you can expect a reply from HMRC