Yes, but make sure you don't miss the deadline to submit your claim because you are waiting for evidence. If you don't have your evidence when you are submitting your EC claim, you should 'continue' through the evidence upload pages in the online system and complete your claim submission.
You'll receive an email confirming the evidence deadline and advising that we can't consider your claim until you've provided your evidence. If you miss the evidence deadline we may not be able to accept your claim - if this happens, you'll be given further information about how you may be able to appeal this decision.
All the information about evidence deadlines and how to access the EC system after you've submitted your claim is on our extenuating circumstances website, which is a fantastic resource for a lot of questions you might have.