When I applied for my MSc I included all of my A-level results in the space provided, despite achieving quite sub-standard grades for my school (B, C, C, D). At the time of applying for my MSc I was still completing my undergrad degree and was on the borderline between a first and a high 2:1 (ended up getting a first). I was told by a tutor at university that A-level results didn't really matter, however when I went for an interview they asked about the discrepancy between my A-level performance and my degree performance. I replied truthfully - when I was in 6th form I had wanted to go into medicine and so taken science subjects that I wasn't good enough at, I then went on to study Applied Psychology and Sociology and did well, and realised that was the career path that I wanted to follow, etc etc. I didn't get offered the place but was later assured that was for totally different reasons, and got accepted onto a better MSc course soon after my rejection.
So I don't think A-level results matter too much, they may well ask about your N grade but with a good predicted degree classification, references and personal statement it shouldn't hold you back too much, particularly if it is in an unrelated subject. Good luck though, what are you applying for?