You do know that British standard plug sockets run between 220V-240V?
The UK mains supply is 240V.
In 1995 the specification
for appliances to be sold throughout Europe was set at 230V +10%, -6% (216-253) so that the same appliances will work across Europe without modification, and without anybody having to change their supply voltage. In 2003 it was further widened to 230V +/-10% (207-253).
Historically the tolerance on UK mains was +/-6% (226-254), but once the new appliance spec had been in force for a while, legacy appliances were presumed gone, and the specification for the mains was changed to 230V +10%, -6%, in 2002. There was still no change in the voltage generated, however, it was just done so that they could allow a higher voltage drop on the lines. There are proposals to take advantage of the full tolerance on the appliance spec, and widen the supply tolerance accordingly, but that's still just a change in what's permitted, not a change in what's actually generated, and not necessarily any change in what's supplied.
This is a plot of my mains voltage from 7.9.23 measured with a power meter and a DMM, including both the nominal voltages, max & min spec limits, and tolerance limits for the two instruments: