[Maarten]

Thanks! The etched number is a Dutch/Belgian sketch number likely to be the same as in Belgian an probably Austrian models, so British production didn't involve a PCB redesign. Unfortunately no clue as to whether the pcb was assembled in the UK or just imported. No labels on the component side of the PCB, I assume?

From the 2 serial numbers (assuming they started counting at 1001) the minimum number of sets produced would be 4181 and the most likely number of sets produced 10655. A production run of around 10000 doesn't seem unlikely but with only 2 examples this obviously isn't a very good estimate.