Servis tumbnle dryer not staying switched on?

I have a Servis Caress M2010 tumble dryer that seems to have stopped working properly.

When I press the on switch, it begins to work, but when I release it again, it stops (it should keep on going until the timer runs out).

I have cleaned the filter, which wasn't that bad to begin with, but I can see lint down inside the unit itself. Is this some kind of safety cut-out that I can cure with a good clean, or will I need to get a new part to effect repair?

Many thaks in advance.