Thanks Josephur I followed your instructions, having to create the "Windows Search" key under HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows with Value "AllowCortana" REG_DWORD 0x00000000 (0) Rebooted, killed Cortana in Task Manager but it still came back.
I followed the instructions but in the Local Group Policy Editor under Computer Configuration -> Administrative Templates -> Windows Components -> there was no Search folder, so couldn't continue. Thanks Chris