Telling prospective employers about mental health

[Orchid19]

I've very recently left my job of 2+ years due to ongoing depression and anxiety which was getting worse by working there. It took me a long time to come to the decision and as much as I feel that I have made the best choice, I still, however, need some form of income. I applied for more temporary work so whilst I am recovering I dont feel too committed to one place. A temp agency called me this morning and wanted to know my availability but then asked why I left my previous role.

I couldn't bring myself to tell them the whole story so I just came up with some stupid excuse about not having support which they seemed to be ok with and asked me to come to an interview next week. I am thinking now, should I tell them about my health issues? I know under the equality act they cannot discriminate me but I've heard so many stories about people declaring their mental health issues and then employers starting to act weird with them and really I just want a job I can do short term with no hassle. I also feel that it would give the reason I left my other job more validity, but then if they decide to not put me forward for the job after the interview I'd imagine it will be more to do with my personality than anything else...

I don't think there's anything legal to say that you HAVE to declare a diagnosed mental health issue to an employer but I'm just in two minds whether to actually mention anything. I'm really not comfortable with interview at all