If you read the UKBA guidance carefully, there is a requirement to mention arrests as well if you have not been told by police that you wont be charged. In your specific case, if you were issued a simple caution, then it is regarded as spent immediately. If it was a conditional caution, then it will take 3 months to spend from the date conditional caution was issued. So please check the paperwork you received from police.
You actually do not need to disclose a caution once it is spent, but in your case, since it is in the knowledge of UKBA, it would be a good idea to explain everything in a covering letter and also include any police paperwork.

Thank you so much for the advice.

I NEED URGENT RELIABLE RESPONSE PLS.
I applied for naturalisation in july 2009 and the application was refused IN Feb 2010 bcos i had an impending prosecution from the police.I was arrested few days before i submitted the application for shoplifting an item worth 12.99, though i was innocent but the police decided to charge me over the allegation. To cut the story short, i was charged to court but the police decided to give me a caution rather than proceeding further with court case. It took so long for the police to arrive at that decision but in the mean time HO wrote to me saying the application has been refused bcos of the charges against me . I DID NOT DISCLOSE THE ARREST WHEN I APPLIED AND I HAVE NOT BEEN TOLD THAT AM BARRED FOR 10YRS.
Now that the issue has been resolved with just a police caution can i now apply for Naturalisation and also should i disclose the police caution and the initial refusal of the application. Thanks URGENT PLS