Q.Will The Chipping From A Leylandi Hedge Cause Any Problems To Plants On My Allotment
I normally spread any chipping around my fruit trees and raspberries canes

Certified GKH Gardening Expert
This can be ok for your plants and trees, since they are deeply rooted. Make sure that they are aged since they do have phenols that will leach into the soil as a defense mechanism for keeping other plants and trees away. Even when they are aged, they will still lower the pH of the soil a bit. I would keep an eye on the nutrient levels, pH, and any toxins that might be built up.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm