UK Voltage

I have noticed that recently the mains supply to my house seems to be creeping ever closer to the supposed max for the UK, 253V (230V AC +10% / -6%). Since I took this photo mid afternoon today, it has hit 250.9V

I found the following quotes on a UK University site. This is suggesting that equipment including hi-fi is inefficient in wasting energy/reducing life at higher than necessary voltages. Does this also have a detrimental effect on what we hear?

Also, listening late at night when the grid is allegedly 'cleaner', music does seem even higher quality (but then again it may just be the effect of drinking a placebic substance at the time)

"It is not unusual for the supply voltage to vary substantially throughout the day. The average voltage in the UK is around 242V. This means that in the majority of properties, electrical equipment is running at a voltage much higher than needed, resulting in excessive losses in many types of equipment. This is due, in a large part that due to the so called harmonisation of supply voltages in Europe all new low voltage appliances are designed to operate at 230V or even 220V. Therefore it can be seen that much equipment designed to be operated at 230V and 220V may be being supplied with a voltage above this if we consider that the UK average supply voltage is 242V, much higher than is needed....if it is still well within the statutory limits, (i.e. 220 Volts) there will usually also be benefits of increased life and reduced maintenance of the equipment...."

It's generally quieter outside at night as well.

Could variations in frequency play a part as well? According to these graphs I found on Wikipedia it does however seem as if these occur all throughout the day and night in most places.
http://upload.wikimedia.org/wikipedia/commons/b/bb/Variation_of_utility_frequency.svg

This just further demonstrates the need for good well regulated power supplies.
There is plenty of information available, but none of it will help if your power supply filtering and regulation is not up to it.
For live info see: http://www2.nationalgrid.com/uk/Industry-information/electricity-transmission-operational-data/ or http://www.gridwatch.templar.co.uk/