I've tried the 'official' method by using bootsect from the Repair option - by booting from the W7 DVD. However whilst the mbr is undoubtabley repaired (one assumes to the original W7 settings) the bootloader used when starting my laptop still boots via Grub. As I finally tried the 'all' syntax with bootsect I have repaired all the Windows partitions.
So I assume Grub is hiding somewhere else (maybe on a Linux partition) and I was looking for help on locating Grub and replacing it with a bootloader from the W7 partition.
Success. I needed to run <BootRec.exe /FixBoot> after changing to the drive causing the problem. As the Command Prompt lands you at the X: prompt I changed Drive to G: and then ran <bootrec.exe /FixBoot>