Joe wrote:
In the process of having a new kitchen fitted, and being told the new
sink has to have 10mm bonding back to the CU. Is this correct? There's
no waste disposal or other mains power to the sink. Water pipes are all
copper.

No, but whoever's telling you (who?!) might be confusing this with a
need to bond the sink to the copper pipes below the taps (would be
thinner cable that 10mm - 4mm IIRC?). Whether that's obligatory or not
is arguable - see lots of threads on this in the archives of this ng
(Christian will argue 'no' on safety grounds, and no doubt he's right;
but - eg - my electrician insisted upon it before he'd issue my safety
report!)

David