The plastic protective cover at the top of the rear shock absorbers (see green arrow in attached picture which points towards where the cover is) has cracked off both of my rear shock absorbers.

Is this something to be concerned about and should I be looking at repairing/replacing anything?

Car's done near 60k on these shocks

You mean the "dust shield" that covers the damper rod (polished steel rod)? If so, then AIUI it's an MOT failure.

Yeah that's the one, thanks

Mine are loose, but didn't fail an MOT due to it..

But i guess it can depend on the tester.

why would it fail ?

not being fitted or having dropped down will not have any effect on the steering, handling or braking capabilities of the vehicle, all they do is stop road debris from damaging the damper rod

have the plastic shields broken/split or have they just come off the bump stops ?

They've cracked off at the top No proper structural damage is there and the car handles fine

all they do is stop road debris from damaging the damper rod

Exactly.