Just received a follow-up letter from my immigration lawyer, regarding my ILR and possible future citizenship. In it he tells me one has to be lawfully resident in the UK for 5 years, at least one of which is on ILR status, before one can apply for citizenship. It would be sooner if my partner and I enter into a Civil Partnership.
I'm posting this to clarify things a bit, in case anyone else out there in an unmarried relationship thinks they can apply after 3 years, as I thought after reading what was posted earlier in the thread. That's not the case.