The switch is an Alpha #SR2612F-0304-18K0B-D8-N, a 3-pole, 4-throw (3P4T) PC-mount rotary switch. However, in the UK, you might have more luck looking for the analogous switch from Lorlin, since they are made there in the UK. I don't have a part # for them, though.
Once you get the correct switch, the real fun begins--de-soldering the 15 connection points on the PCB. You'll need a good "solder sucker", some de-soldering braid, and a generous helping of patience for that. Take it from one who replaced exactly that switch on exactly that pedal.
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