When I was collecting two years worth of documentary evidence about me and my partner living at the same address, I got various opinions from different forums and home office hotline. With my personal experience you need 20 letters (almost one document for each month for the 2 year period) with both names addresses (partner and yours), but in case if you do not have everything with both names together, you can produce two separate files, one file for your documents addressing only your name and another file with your partner's documents.
It is not essential that both must show bills etc but when you are collecting, make sure that both files separately have 20 documents from ‘Five’ different sources. The best sources in my opinion home office will accept are county council bills with both names addressed. If for some reason you forget to save your bills, just call county council to get the copies of the bills. You can also use electoral register entry to prove that both of you are living on the same address. You can ask your doctor to provide you a letter about how long you are register to their surgery. If you are living on rent, contract between you and your landlord will be very useful and authentic. If you or your partner have a mortgage, documents about mortgage can give provide a solid foundation for your financial commitments together. Payslips with your home address are another very useful and authentic document.
FLRM AND OTHER DOCUMENTS:
Apart from these 20 or 40 documents, you need FLRM form along with your last three months bank statements, last three months pay slips (If you are working). I also have taken my partner's pay slips (last three months). You need two photographs of yourself, one photo of your partner. Your passport, your partner's passport (if he is British national and don't have passport, his or her driving license).
Obtaining a UK Unmarried Partner visa is fairly straightforward if you have the right documents. WRONG !!! . Be ready to book another appointment in case you can't spare 5 minutes to read these
1. UK UNMARRIED PARTNER VISA (DEFACTO VISA) FOR INTERNATIONAL STUDENTS and
2. UK UNMARRIED PARTNER VISA (DEFACTO VISA) APPOINTMENT