[SOLVED]VirtualBox VT-x stopped working since QEMU installed

Hello All.
I have been happily using VirtualBox for many years but thought I'd try using KVM through QEMU as I'd read some reports that it can be faster. This was a mistake as I now find that any VM I have in VirtualBox that is configured for multiple processors, and therefore needs to use VT-x, no longer works.
I get an error "VT-x is being used by another hypervisor". I presume this means that some part of QEMU/libvirt is still running even when I have nothing started in the Virtual Machine Manager. Do I have any options other than uninstalling QEMU?
I have been happily using VirtualBox for many years but thought I'd try using KVM through QEMU as I'd read some reports that it can be faster. This was a mistake as I now find that any VM I have in VirtualBox that is configured for multiple processors, and therefore needs to use VT-x, no longer works.
I get an error "VT-x is being used by another hypervisor". I presume this means that some part of QEMU/libvirt is still running even when I have nothing started in the Virtual Machine Manager. Do I have any options other than uninstalling QEMU?