What kind of bottom bracket fixing is this? Dismantled my bike to try and take a look at the crank bearing, as I fear it may be getting dry. Unfortunately at the stage pictured I could go no further.

The outer and inner rings appear to be separate, and locked against each other (presumably to set the end-float of the axle?). No idea what kind of fixing this is, so also no idea what sort of tool is required.

Does anyone recognise it?

Thanks!
That's the chain guard bracket and it would likely come off with a bottom bracket lockring tool. The fixed cup of the bottom bracket should be behind it.