QUOTE
The Highway Code says:
188
Mini-roundabouts. Approach these in the same way as normal roundabouts. All vehicles MUST pass round the central markings except large vehicles which are physically incapable of doing so. Remember, there is less space to manoeuvre and less time to signal. Avoid making U-turns at mini-roundabouts. Beware of others doing this.
Thus if one is unable to pass around the central markings it would be in breach of the law - And a Poojoe three double oh eight cannot get around without causing other road users to have to stop because he's an idiot and can't be arsed to drive another 800 yards up the road to a proper roundabout.
I would assume that if you can get your car round a mini-roundabout whilst
1) Stay within your lane,
2) Not Reversing
3) Not causing a hazard or danger to other Road users (OR pedestrians)
Then you are driving within the rules of the road. However if you can't do that, then you are driving outside of the rules of the road and thus doing a 180 at a mini roundabout is illegal.
I, for example, cannot get around the mini roundabout by Craven Road in Newbury, so I have not even ever tried. Unlike said Poojoe driver