You got me on the right track and I have fixed the problem. The link you gave me was useful and I tried the repairs and the purge re install as suggested, but no effect. Within the link you sent was another link to a GRUB 2 repair tool for Ubuntu.
Before I did a reinstall as I was planning I thought I'd give it a try as MINT is an Ubuntu "derivative" if that is the right word AND it claimed to work from a Live CD.
The great news is that it works OK with Mint 11 AND it fixed the problem I was having with one click! To save you looking for the information I have copied the instructions from YannBuntu's site to install the boot repair application, you can do this for a HDD, Live CD or USB boot:
sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update && sudo apt-get install -y boot-repair && boot-repair
Thanks again Andrew and thanks YannBuntu