Following a tip from Ian last night I measure the drop in voltage when
switching on a higher power device.

Prior to running an electric shower I was seeing 247 volts (it fluctuates
quite a lot up to 248V). With the shower on it dropped to 234V. This
seemed like quite a large drop, does anyone agree?

I'm not dure of the rating of the shower, so I repeadted the test with a
2.4KW fan heater. This time the voltage dropped from 247V to 240V.

I'm going to give the electricity board a call, but would welcome any
feedback.

Cheers,
Chris