Loaded Spring (NN8 Wellingborought)

Wanted - anyone out there who had purchased a Challenge 18V Li-ion Cordless Grass Trimmer in the past from Argos. Where the Spool Head is we have lost our loaded spring which holds everything in place to cut grass. Unfortunately do not know the size dimension of the spring. If you have any loaded springs or had purchased this in the past. Would be grateful if you can help. Thanks for reading this post.