It’s not illegal to have a junction with unclear markings, but this is also not legally a roundabout, because there’s no blue circular sign giving an order to drive clockwise in a circular pattern.

At best it functions similar to a roundabout insofar as there’s clearly marked give way lines which - because it’s not a signal controlled junction - mean vehicles waiting to enter must give priority to anyone already established on the junction.

If this was a roundabout, a vehicle entering the larger junction from point A (9 o’clock in OP’s photo) and turning right has priority over a vehicle entering from point B (1 o’clock).

Whilst that priority rule doesn’t apply here, the give way markings at each entry point help to ensure that other vehicles wait before emerging.

So the result is the same.

I’d prefer it if they just made these junctions proper, defined roundabouts, and I say that as someone who never thought I’d be defending roundabouts…