http://www.ukba.homeoffice.gov.uk/britishcitizenship/eligibility/registration/britishnational/
Can I register as a British citizen if I have some other form of British nationality?
This section provides details of the requirements you need to meet for us to register you as a British citizen using application form BOTA.
You will be able to register in this way if you are:
•a British overseas territories citizen; or
•a British overseas citizen; or
•a British protected person; or
•a British subject; or
•a British national (overseas).
Registration under this provision gives citizenship otherwise than by descent. This means that if you register as a British citizen in this category you will be able to pass this citizenship to any children born abroad to you after registration.
You should read the information in this section before you make an application for registration. You will need to pay a fee when you make your application. If you make an application for registration and it is unsuccessful because you are not eligible, we will not refund your fee.
There are three ways you can be eligible for registration as a British citizen otherwise than by descent. These are:
•your residence in the United Kingdom; or
•due to your time spent in crown or similar service; or
•you meet the alternative provisions for British overseas territories citizens.
The details of how you can meet the eligibility requirements are set out below. You only need to meet one of these three requirements.
If you meet the requirements for registration you should go to the applying section for details on how to apply.