Cannon House, also known as the Parish Centre and the Saint Monica’s Social Club, is used by SMP for rehearsals and to store costumes. It is also used by the Church and other groups.
The Parish Centre have their own website here: http://www.stmonica.co.uk/Parish%20Centre.htm
The address is:
St Monica’s Social Club
6 Cannon Hill
London N14 7HG
Here is a map of Cannon House via Google maps.
A photo of Cannon House: