The different numbers are the sts to work for the different sizes. So if your size has a 0, do nothing. Ignore that instruction and go on to the next one. It’s not just UK patterns that are written this way either, many US ones have this notation.
Thanks Suzeeq - I thought it needed to have something to do with sizes, but it just seemed weird that it would alternate like that rather than go up or down per the size. Any thoughts on K0 or repeat to the last 0?