I am assuming you live in UK and have spent 3 or 5 years to get your Nationality.  If this is true you need Form AN(NEW)

Also make sure you read about Dual Nationality Condition as an Indian National on the Home office site. I am not an Indian but I read something that Indian National may not be able to keep both Nationalities. Here is the text from Home Office site. Please do your own research also:

6. Dual nationality
http://www.ind.homeoffice.gov.uk/ind/en/home/laws___policy/policy_instructions/nis/chapter_14/annex_h.html

6.1 Indian citizenship cannot normally be held in combination with any other citizenship. Section 9 of the 1955 Act provides that

"Any
citizen of India who by naturalisation, registration or otherwise
voluntarily acquires.....the citizenship of another country..... shall,
upon such acquisition,..... cease to be a citizen of India".

6.2
This means that no adult (18 and over) can hold Indian citizenship in
conjunction with any other nationality or citizenship. This applies
irrespective of whether the person holds any passports (either Indian
or that of their other nationality/citizenship).

6.3 Further, if
an Indian minor obtains another nationality or citizenship (for example
by registration as a BN(O)) the child will automatically lose its
Indian citizenship. This applies even where the registration is made by
the parents/guardian on behalf of the child.

6.4 The only
exception to this general ban on dual citizenship is where a child is a
dual national by birth. In such cases that child can remain a dual
citizen until either:
a. they obtain a passport in their other citizenship (while under the age of 18); or
b. they reach the age of majority (18)

6.5
If a child who is a dual national by birth fails to renounce their
other citizenship prior to reaching the age of majority or acquires a
passport in their other nationality before reaching the age of 18 they
will lose Indian citizenship.

I have come across various forms on the home office website and I am in bit confused.

Can any one help me out which form I have to fill, Is if Form AN(NEW) or Form  B(OTA) or Form B(OS).

Note : I am an indain holding Permanent Residence visa.

Thanks,

Kumar