Hoping somebody can help? on my last 3 rides the rear mech long arm has what I can only describe as sprung up towards my frame and stuck in that position which in turn stops me from pedalling; after getting off the bike flicking through the gears then turning the cranks it seems to right itself. I was wondering if it is a chain problem or the rear mech beginning to fail?

Appreciate any help!!!

Sounds like the bolt that fixes the mech to the frame needs a good soak in oil.
Do not take the c clip of that holds it all together. The gates of hell await if you do.
Edit if it’s a modern mech try the bolt next to the one that holds it on
Edit edit have looked at my modern mech and it’s probably not that! Sorry.

Maybe your mech is too happy

I’m going to suggest chainsuck, there’s not much else that’s going to pull the mech’s cage forward like that.