I decided to take the drums off, to clean out the dust, and check the cylinders were ok. That's when I had a bit of a shock on the passenger side.
One of the springs had snapped, so the shoes weren't returning properly.
Here's a pic of the shoes I replaced.

Looks like they were getting a bit hot!!!
I'll always be taking the drums off when I adjust the brakes from now on. You never know what's going on in them.