From the looks of it, a MK3. Better view would be from inside, but the MK3 knob is what I see. The mk1 and mk2 have almost the same knob, but the mk3 has a Bakelight knob, like yours.
A quick referance is this.
MK1 has a round switch, all plastic.
MK2 has a square switch, all plastic.
MK2 is...