AFAIK the only real fix is for the DNO to change the tapping on the transformer supplying your (and other people local to you) 230V. Obviously there is a cost to this,so they won't do this until they have to. You have to keepttelling them that your supply is over 253V, that they are not meeting their specification and customer obligation and that you are concerned the overvoltage will cause damage to your local equipment (higher voltage means things with electronically controlled power supplies such as kettles will draw more power at 253V than they do at 230V). Eventually they will give in and install a monitor at your house, and confirm (or not) the overvoltage and then go and changed the tapping on their supply transformer.
Of course, part of the problem is that folks with PV systems feeding power back into the grid are pushing the voltage up a little (otherwise the power won't flow out of your house and into the grid). An inverter will raise the voltage no more than about 2V when it is feeding back into the grid. But if lots of people are all doing that then this does not help the DNO hold the voltage within their -6% to +10% on the nominal 230V. However, the fact that you as a PV owner are pushing their voltage up is not an allowed reason for them to be over voltage though.
Persistence seems to be the key technique. Sorry, if you already knew all of this - I don't think there is a magic bullet..
