If you require the classic UK2000 Common Library for the legacy products (FSX,FS2004,P3D) then here is the link
https://uk2000scenery.com/Common_Library_Package_3.74.exe (https://uk2000scenery.com/Common_Library_Package_3.74.exe)
In rare situations, the scenery package may also fail to download the 'UK2000Installer.exe'
here is that link for that:
https://uk2000scenery.com/UK2000 Installer.exe (https://uk2000scenery.com/UK2000%20Installer.exe)