Thanks for all the responses.
I have sent email to firstname.lastname@example.org
with subject "Updating Personal Information" including my address, mobile no, name, home office reference, place and date of NCS.
I also included this "I got a simple caution from Police on 12/01/2014 for Common assault. I am attaching the scanned copy of the report."
and attached the scanned copy of the caution that I received.
I sent this email on 14/01/2014. Today (15/02/2014) I received a letter saying that my application was rejected based on the same.
It also says this which makes me worried
"It is open to you to re-apply for citizenship at any time but your failure to disclose a conviction to us will be taken in to consideration on any fresh application made within ten years of the date of this letter and is likely to lead to the application being refused."
I thought I can reapply after three years but it says my application will be rejected for ten years.