Is honesty the best policy?

When asked about gaps in my cv, and reasons for leaving my last job, should I give them a convincing lie (or rather selective truths), or should I be honest about my history of depression and that I want to leave my current job because the hierarchy and personnel department did not treat me fairly as a person with a disability?

I have a couple of applications out and I am hoping for an interview from at least one of them and I need to be prepared for how to appoach this subject.

Bagpuss