Checked the memory of my phone yesterday.
I’d used up nearly all of my memory, 10GB out of the nearly 12GB available.

Checked again today, and the phone is telling me I’ve only used 5GB.

Eh?
Haven’t deleted any apps, just listened to some stuff on the iPlayer and downloaded newer episodes to replace them?

Have I deleted something by accident, or have some apps I don’t use been automatically uninstalled?

Might have been a load of cached data that the OS decided to delete for you.

Possibly, but I did that myself a few weeks ago when I realised I was running low.