UPDATE - got a response from ap-suspensions.co.uk , which turns out to KW , they asked for the part numbers off the strut but I was able to give them the number on the spring as well - 60181062.
Spring is £62 + 24hr courier at £10.40, better than having to replace the lot and they were very helpful , so don't panic if you've got ap's and you snap a spring , you CAN get replacements.