Problem is, although it's quite a fluctuation it's still within the
limits so they won't be overly bothered.

You were right, although I was fairly impressed as they were willing to make
an appointment if I really wanted to. I decided to hold off for now.

I still don't know what type of supply you have, what size it is and
how old it is but if it's an oldish overhead then what you're seeing
is the norm.

It's not an overhead, it appears to come from underground. I don't know
whether this is relavent, but when we first moved in the meter and main fuse
were exposed to the outside air (albeit under a small porch). I managed to
get the board to fit a plasit enclosure a while back, but one of the items
picked up by the electricians report was that the fuse looked quite worn. I
still have a slight problem here as the isolator switch is still exposed -
I'm trying to find a lockable replacement.

The only way to solve it is run in a new 100A underground
supply but that could be costly. Even then it depends on how far from
the substaion you are.

Thanks again for your advice. I guess the main thing is that I know it's
not dangerous. I may ask them to come out and check it to play safe.

Cheers,
Chris