Podcasts deleted from iTunes still on my iPod

I have an iPod Classic and mostly listen to podcasts. After I have listened to an episode I delete it, but some episodes are still on the iPod. I can't delete them by deleting them from iTunes and then syncing as they don't exist in iTunes; when I connect the iPod and navigate to the relevant Podcast on the iPod using iTunes there is no option to delete it. The episode is really there as it can be played on the iPod. I have tried downloading the episode again, re-syncing it, deleting it from iTunes and syncing again, but it's still there on the iPod!

Help! How do I clean up the iPod and get rid of these old episodes that are cluttering it up?