After another evening of testing, I have managed to resolve this issue.
Once the installer gets stuck at ‘Creating Shortcuts’, the only solution is to reboot or end task the installer process. Once this has been done, try running the 4.2 help installer. This will offer to rollback changes made by the stalled 4.2.0.4 main installer.
Once uninstalled, remove all LibreOffice folders (if there are any) including anything left in the start menu. Open a cmd window and type %temp%. Clear this directory.
Try to reinstall LibreOffice again and the installer went through. It is also possible to get the install to write out a log file to see if it gives anything away, although for me this was not required.
The command to do this is :
msiexec /i LibreOffice_4.2.0_Win_x86.msi /Lv LogFile.txt
This should be run from the drectory containing the installer and will create the log file in the same folder.
Hope this helps someone else.