Mission control desktop created on every startup

Hello!

I have noticed that for months on end now, everytime I turn on my Mac Mini, a new desktop is created (accessed via Mission Control). As you can see from the snapshots before and after a restart below - this is getting rather ridiculous - and I'm sure it can't be doing many favours for speeds too.

Btw - pretty sure it occurs on every startup - can't be 100% sure though.

Any help would be very much appreciated!

Max