Overall, the main objective is to convince the UKBA (as a reasonable person) that you are not acting fraudulently. If you've something that's not listed in the details below, but that would help prove the relationship, I'm sure you can include it. In my experience, we included letters and emails from family and friends referring to us as a couple; joint invitations to events like weddings; and photos of us on holidays.
EEA Family Permit
For the EEA family permit, the current guidance is at Home Office Extended family members of EEA nationals document. See Page 13, "Evidence required for durable partners":
The applicant and the EEA national sponsor must have been living together in a
relationship similar to marriage which has subsisted (continued in existence)
for at least two years. The evidence the applicant can provide may include (but is not limited to):
- Proof that any previous relationship has permanently broken down:
- degree absolute for marriages
- dissolution order for civil partnerships.
- Evidence of cohabitation for at least two years:
- bank statements or utility bills in joint names at the same address
- rent agreements
- mortgage payments
- official correspondence which links them at the same address.
- Evidence of joint finances, joint business ventures and joint commitments:
- Evidence of joint responsibility for children such as a birth certificate or
custody agreement demonstrating that the two parties claiming to be in a
durable relationship are cohabiting and sharing responsibility for children.
- Photographs of the couple.
- Other evidence demonstrating their commitment and relationship.
You must always consider the individual circumstances of the application
and consider whether it is appropriate to use discretion. For example there
may be instances when the two year rule is not satisfied but the couple have a
child together. In these circumstances you can use your discretion if there is
enough evidence. For example, a birth certificate showing shared parentage
has been provided with evidence of living together.
You must refer to a senior caseworker if you doubt whether the level of
evidence provided is enough to demonstrate a relationship exists.
If the applicant has provided enough evidence and you are satisfied that
the documents are genuine, you must consider whether the requirements of
regulation 8 of the Immigration (European Economic Area) Regulations 2006
(as amended)(‘the Regulations’) have been met before you go to stage 3.
The EEA regulations referred to do not cover specific types of evidence.
ILR and Other rules
As there's some ambiguity about the question, it's worth noting that for other visa types there may be differences in the rules. However, the list above should almost certainly cover you. The EEA regulations linked to above will NOT apply in these cases though.
For more details on those cases, consider posting a new question, or visiting: