There is no strict two-year rule for such unmarried partners: the migrant concerned only has to demonstrate that there is a “durable relationship” – but of course a lengthy cohabitation is useful evidence in such a case”.
Is this not a prerequisite???
Answer: Under UK immigration law, specifically the Immigration Rules, the basic requirement for an unmarried partner is that they have been living with the settled partner for at least two years. In fact, to put it a bit more strongly, if you have been living with the settled partner for at least two years (and you can prove it) this may be enough to get you the visa.
EU law works differently (and the terminology is different: “durable relationship”). There is no two-year requirement anywhere stated. Of course if you have been living with your partner for at least two years this may help you make a strong application. And, conversely, if you have only been living with them for a few months then it may be a weak application. But if you have been living with the settled partner for a substantial period, but of less than two years, you could still succeed, and especially if you good documentary evidence generally about the relationship.