Having assessed this circuit further the controls side is only a few volts. The Thyristor and rectifying part of the circuit is the only part carrying mains.
Nigel: I thought looking at it it was a lamp dimmer but the SCR in that circuit is a 5A unit. Even a 250W lamp is only roughly 1A.
I am building it regardless as it is temperature controlled and provides a dimming effect O/P. Accuracy on the control side of things may need some work.
Illconductor: I am a fully qualified electrician aswell as electronics engineer. A dimmer installation will be no problem.
Thanks for the replies lads.