I’ve tried inprivate browsing and clearing all cache.
Having done a bit more research it seems the flickering is a known issue in Edge, and can be caused by incompatible apps, in particular Norton AV, iCloud and IDT Audio are known to cause this issue. I don’t have any of these apps on my system but it could be another app. So it does appear to be just an issue with my system and hopefully my family members PC will confirm this. I just find it really strange that it doesnt do this with ANY other sites.
Incedently, I have just discovered that IE11 is also still included in Windows 10 and I’m happy to say there are no issues at all with the site with this browser.