If you are using iCloud, on your iPad tap Settings > iCloud. Tap Photos then switch My Photo Stream off then back on.
On your Mac open System Preferences > iCloud. Deselect the box next to Photo Stream then reselect it.
Give iCloud a few minutes to re sync your photos.
Thanks, Carolyn, but that technique, regrettably, didn't work. I still have multiple duplicates on the iPad.
On the iTunes page I don't see any way of deleting photos from the iPad; surely there must be a way?
Will keep looking.