NT,

16mm2...

OK, thanks for that.

...and it must be earthed within 2m of the sink,
so you may have to take a tile up to get an earth
rod in as well.

There's no earth anywhere near two metres of the sink in any direction
including straight down. Does the sink have to have a *direct*
independent connection to actual earth? The rest of the internal
copper pipework is earthed back to the consumer unit (in very hefty
cable, which I take to be 16mm2) and thence to the incoming supply's
earth; surely it would be sufficient to bond the sink to the nearest
available copper pipe?

Bert
http://www.bertcoules.co.uk