It's an early-ish range. Post-Harris, but, I think, pre-'75, when Said took over and other splodgy designs were used, but not nearly as complex as this one. I suspect Dobson might be the designer.
Both yellow and orange are difficult colours to work (they misbehave) - and in this design, there is a yellow splodgy background, but it has been trailed with clear glass covered in orange splodges.
The later splodgy designs are mostly a white background, with a small patch of one or two colours applied - or just splodgy all over.
I think a lot of pieces in this design went to Germany. They don't turn up too often - and are often in Germany when they do.