Process of elimination leads me to believe that the Toshiba Hotkey Driver update installed by Windows Update breaks certain key mappings. Unfortunately it is not possible to uninstall the update. The only option is to disable the four relevant entries in Device Manager > Human Interface Devices but it doesn't fix the keyboard mapping issues. If you Uninstall using Device Manager the entries reinstall after a reboot.
Known Incorrect Key Behaviour
Number 1 key above letter keys (not numpad) = Have to press FN+1 to type number 1 numeral
Number 2 key above letter keys (not numpad) = Have to press FN+2 to type number 2 numeral
Number 3 key above letter keys (not numpad) = Have to press FN+3 to type number 3 numeral
Number 4 key above letter keys (not numpad) = Have to press FN+4 to type number 4 numeral
To insert a ! or " or £ or $ then you have to press FN+SHIFT+required key.
Files listed are:
This laptop is not on the Toshiba authorised list of laptops compatible with Win10 however everything works perfectly with out this update.
As a side note there is no BIOS setting to change FN Key functionality and there is no key combination e.g. FN+F11 or FN+NumLock to toggle the functionality. Basically the FN key is ON by default when it should be off!