Walking through to the back of the Peace Garden, turn left then almost immediately right down Endsleigh Street. After two or three minutes you will come to Tavistock Square. Cross over Endsleigh Street and enter the garden in the middle of the square. On your immediate right is the memorial to the conscientious objectors – a great slab of slate bearing an inscription, with a bed of white roses planted behind it, and (sometimes) flowers with the names of individuals or groups of people who are commemorated by visitors.
Further information can be found here.