NHS Website
The NHS provides guidance on a variety of topics. One of the topics is returning to work after mental health issues.
http://www.nhs.uk/Livewell/mentalhealth/Pages/returning-to-work-mental-health.aspx
GPs can provide a fit note which explains how your condition affects your ability to work which can aid employers in understanding how to help you in your return to work or how to help you stay in work.
http://www.nhs.uk/Conditions/stress-anxiety-depression/Pages/improve-mental-wellbeing.aspx