The steps for applying for British dual citizenship are essentially the same as those for applying for basic British citizenship. The only difference is that the former entails keeping citizenship in your native country, whereas the latter might include revoking your former nationality. Because Great Britain does not require that you revoke your former citizenship, you are free to keep it.
Ensure the country in which you are a national will allow dual citizenship. Some nations will revoke your citizenship if you become a citizen of another country. Before applying to become a British citizen, contact your nation's consulate or embassy to find out if your current nationality will be affected.
Determine your eligibility. You have a number of application forms to choose from depending on your status as a noncitizen, a British national, a British subject, a British overseas citizen, someone married to a British citizen or someone in the service of the Crown within the U.K. or abroad. Various age and residence requirements apply, depending on your status.
Choose an application method. You may apply through the Nationality Checking Service, through an agent or representative registered with the Office of the Immigration Service Commissioner, or individually. If you apply individually, you must supply original documents or fully certified photocopies of originals. The particular application form you choose explains which documents you must supply.
Pay the application fee. The fee varies depending on the type of application, with lower costs for simply confirming your citizenship status and higher fees for spouses applying jointly. The fee must be paid in full at the time of application.
Wait for your application to be processed. The U.K. Border Agency will confirm receipt of your application within four weeks. Processing can take anywhere from three to six months, although in rare cases it may take longer. If your address or marital status changes during this time, or if you're the subject of a criminal investigation, you must notify the Border Agency of these facts.
Attend the citizenship ceremony. If your application is approved and you live in the U.K., you'll receive a letter of invitation to attend a citizenship ceremony. You must arrange to attend this ceremony within three months of receiving the invitation or you will have to reapply for citizenship. At the ceremony, you make an oath of allegiance to the crown and a pledge of loyalty to the U.K. You also receive your certificate of British citizenship along with a welcome packet.