Does a women revert to Islam have to observe an Iddah period from a previous unislamic marriage?

I reverted to Islam in April this year. Prior to this I had been married to a non muslim but this marriage broke down several months before my reversion. I am currently getting a legal divorce through the UK courts. My question is do I observe Iddah for this unislamic marriage and if so when from? The date of speration (before reversion), the date I reverted or from when I get my legal divorce? May Allah reward you for your good work.