If both parties lived outside the UK they qualify while one party could be a UK citizen and the other from another country too. In this instance, one could apply for unmarried visa partner, but the individual will be required to meet the set financial requirements.
Prior to applying for an unmarried partner visa, adequate accommodation must be set up for the applicant and the applicant must be financially stable. If the applicant cannot support himself or herself the other partner must be capable of supporting him or her.
Good news for same-sex partnerships is that the unmarried partner visa applies to same-sex partnerships too.
In addition is there no restrictions like work or opening a business when staying in the UK with an unmarried partner visa. In cases where applicants have lived together for under four years the visa will be valid for a two-year period. When they are still together after the initial two-year period, an application for indefinite leave to remain can be applied for.