If you are the spouse of a British Citizen AND you now have Indefinite Leave to Remain then you may apply for your British Citizenship (Naturalisation) on the basis that you have been here in UK for 3 years.

Please do read this UKBA webpage - How do I apply for naturalisation as a British citizen?

You can see and download the form and guide from the RH side of the page.

Here are the requirements and eligibility - Requirements for naturalisation if you are married to or the civil partner of a British citizen

You'll notice the residence requirement states:-

In order to demonstrate the residential requirements for naturalisation you need to:
have been resident in the United Kingdom for at least three years (this is known as the residential qualifying period); and
have been present in the United Kingdom three years before the date of your application; and
have not spent more than 270 days outside the United Kingdom during the three-year period; and
have not spend more than 90 days outside the United Kingdom in the last 12 months of the three-year period; and
have not been in breach of the immigration rules at any stage during the three-year period
The start of the 3 year residency is when you arrived into the UK (even that was as the holder of a fiance(e) visa)

Good Luck

Almost completed your immigration journey