If you are asked if you have ever been convicted of an offence then you would have to answer yes. It might not appear on your disclosure but they have asked if you have ever been convicted, to which you have.
Surely it would be better to be completely honest with a potential employer than not?
There's potentially 3 scenarios.
Firstly you declare your past conviction and they reject your application.
Second, you declare your past conviction and you get the job.
Third, you don't declare your conviction, get the job, then they discover this past conviction which could then mean you losing that job.
Maybe that's just how my mind works, but personally I would declare it and be honest.