There is a defibrillator located here inside a yellow casing, wall-mounted to the building to the right of the Saint John's Scotland building and garden, when you approach those from the opposite side of Saint John's Street.

It is outside of the garden/fenced area.  I plan to map it soon, and would like to confirm some details from the recommended tag keys on the OSM wiki first.

I may attempt to photolink this too; I have an existing WikiPedia account, so perhaps Commons is the way to go, if such a photo would be within policy there.