clangers wrote:
What is the accepted way to extend the incoming main? Henley blocks or
something more substantial?

It must be a single continuous cable, no Henley blocks or similar
as they are points where unmetered electricity can be taken from.
To comply with your electricity supply contract who-ever moves
your meter must:

- cut the sealed links and remove the incoming supply head fuse
* NOTE - THIS MUST NEVER BE DONE IF THE INCOMING SUPPLY
* HEAD IS A CERAMIC FUSE HOLDER AS IT WILL FALL TO PIECES.
* STOP AT THIS POINT AND BOOK A SUPPLY HEAD REPLACEMENT.
- disconnect supply tails from the supply head
- cut the sealed links from the meter
- disconnect the supply tails from the meter
- move the meter to its required new position
- connect the supply head to the meter with continuous,
unbroken lengths of supply tails of required CSA for
the installation (usually 25mm^2, though some are 16mm^2)
- replace the incoming supply head fuse
- replace the sealed links

JGH