Thanks for the welcome people.
N4RPS, I can understand how people might have problems, especially those who've never used anything but Windows before.
I thought I understood the guide ok, it seems easy enough to follow, some past experience installing Ubuntu helps, though I'd never tried to set up a dual boot until now.
I think my mistake was not following the troubleshooting link in the guide when the installer didn't offer the option to install alongside Windows, and not enough sleep at the time
From memory I think I just checked the LVM option thinking that it sounded good & didn't see the Erase Disk button was set as well.
Whatever I did by the time I realised it was too late, even though it was only a few seconds until I tried to stop it
In the end I had to use the Something Else option & set the partitions manually as trying the other options all failed after this with an error but I can't remember what it said.
Installing from a USB I was, once I set the partitions manually all went well.