Got very useful input from here last week - thanks again.
My home electric circuits were tested as ok some weeks ago, including
adequate earthing, when a survey was done for a new combi boiler. When
they came to fit boiler, this was abandoned when initial tests showed
earthing inadequate - nearly 5 ohms instead og 1. In the interim new
street mains and house supply gas pipes were replaced with plastic and
one possibility is that my equipotential bonding to old iron gas pipes
was helping earth my system, instead of gas pipes being earthed to my
system.

Impedance of about 5 ohms was measured at earth connection on sockets.
Same was measured at what was supposed to be the actual main earth; an
earth wire from the consumer unit - what I call the fuse box!! - to an
ordinary earth clamp (http://www.ultimatehandyman.co.uk/
earth_clamp.htm) round the pipe containing the incoming mains
electricity supply. The theory, by both British Gas (boiler fitters)
and Scottish Power (DNO for my area) is that the earthing supplied by
this pipe is inadequate or has become compromised.

One electrician did try scraping the pipe a bit at this earth
connection to get a better connection, without success. However, I've
since noticed that what looks like copper is more like some ancient
gunge/paint/corrosion which I've scraped down to a shiny metal surface
and re-attached the earth.

I'd like to now measure the earthing impedance at this earth
connection down the pipe and, if possible, at the sockets. After
initial crude tests with 'socket and see', I think electricians
previously tested it with multimeter.
I know enough about volts amps and ohms to know what they are, but
don't usually touch electrics - but I do enough about electrics to
know what not to try!!

What I don't understand is how to find impedance down earth pipe and
at socket with a multimeter. I'm not measuring the resistance across
something but down something where I dont have access to the other
end. Do I attach attach one probe to something non-conductive and the
other to the pipe to get the resistance to leakage in one direction,
and how do I safely get a reading at socket (and no, I do know enough
not to poke into the live supply).

There is a delay in the DNO attending - I'd be interested to know
whether things are safer meantime and to what extent what one
electrician saw as the possible problem, might have been corrected.

Regards

Toom