BigWallop wrote:

[of distribution network operators]
[...] They test for correct earth-loop impedance, voltage drop across
the mains conductors under differing conditions and other safety
device tests.

As Colin Wilson has already said, "they" no longer routinely do any
tests on a consumer's installation. In fact they haven't done so since
the 1988 Electricity Supply Regulations (since superseded) came into force.

They will expect to see a fully completed and signed electrical
installation certificate (as detailed in BS 7671) before connecting a
new supply. To see what's involved you can find the blank forms at
http://www.iee.org/Publish/WireRegs/Forms_2004.pdf.

--
Andy