Only a court can decide if you are covered by DDA or not, however, your occupational health provider should be able to indicate as to whether they think you would be covered or not. Each case is different, I have been told by Occupational Health that I am 'likely to be covered' therefore my employer treats me as if I am covered. But a colleague was told she was 'unlikely to be covered'.

From memory you don't have to disclose your depression as a disability, if applicable you would still be covered by DDA.

I'm from Scotland too so I'm quite familiar with procedures etc. Feel free to PM if you need to.