OP
Geordie Spark
I havent read all the posts!! but when I did my 16th edition and test and connect course years ago I was told that even though you may have a 60/80 Amp head at the time, the DNO may upgrade their service to 100 amp, therefore its prudent to fit 25mm tails.
I rewired my house recently - in fact, truth to tell, it's still ongoing - but I fitted 25mm tails from the new 15 way main switch + RCBO'd board to my isolator.
From the isolator back to the meter, & from the meter back to the cut out, the tails are the "old coloured" 16mm. Then the bloke came to change the meter not asked for by me, but sent by DNO and I handed him a nice new pair of tails & asked him to fit them in place of the old 16mm pair.
He refused, claiming it wasn't his job, so I now have what I think is the ludicrous situation of having 16mm "old coloured" tails from the cut out as far as the isolator, & then 25mm tails from the isolator to the CU.
The mind boggles !!!!