UPS - Not the postal service rather an Un-interrupted Power Supply
It should regulate the output voltage.
How long have you been having problems? Does you House and Street have a lot of Solar panels on the roofs? This can cause the voltage to rise.
The problem is (and it is a fault by Renault) UK voltage can legally go up to 250V before the grid has to fix it. However the charger has problems over 248V.
Try different times or the day and at different places. Often the over Voltage is localized.
I think it very unfair that Renault expect you to pay for a Voltage regulator for a design fault by them.