It's supported by the leaders of all three major parties in the Commons and can apply to prospective candidates and their campaigners and supporters at all levels of government. Despite this, none of the three parties seem to have (so far) said anything centrally about it, so it appears that they're all leaving the decision as to whether to sign up to the compact to individual candidates.
I'm therefore sending the following letter, or a slight variation, to each of the local candidates (so far, Conservative, Labour, Liberal Democrat and UKIP).
The All-Party Parliamentary Group on Mental Health, the Royal College of Psychiatrists, and the charities "Rethink", "Mind" and "Stand to Reason" have recently released an "Election compact on mental health". The full text is available as a PDF at http://www.mind.org.uk/assets/0000/7488/election_compact.pdf
This compact is an undertaking to not stigmatise, slur or discriminate against anyone with a mental health problem, to challenge negative attitudes towards mental health, and to represent the interests of all your constituents regardless of their mental health. It is supported by the leaders of all three major political parties, and is open to candidates at all levels as well as their campaigners supporters to sign up to.
Will you, as the [party] candidate in [constituency] for the coming general election, be signing up to this compact and requiring your campaign team to follow it also? If so, will you make a public announcement of this? If you will not be signing up to the compact, why not?
If I get any replies I'll mention them in the comments. I'll also, obviously, be carefully watching election publicity to see if the parties follow the compact or not, regardless of whether they formally sign up.
I encourage you, if you're in the UK, to write to your own candidates - ask in comments if you need help finding out who they are or how to contact them - to ask them to sign up too, if they haven't already.
Rethink also have a petition related to this to ask the next government to take action outside the campaign too (UK residents only).
Those of you outside the UK - is there anything similar available in your elections? If so, do many candidates sign up to it, and do they stick to it if so?