A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
This problem has now been resolved by Microsoft Support. The issue was due to excel registry settings left over from previous Office installations. I assume this is why the problem didn't occur in Safe Mode - apart from disabling Add-Ins it was also disabling these registry settings. The solution involved deleting Excel, removing all registry references to Excel and then re-installing Excel. Thanks to those who suggested solutions.