I think Paul (Cornwall) might be refering to your cables being round, making them look similar to 3-core flex from the outside.
Our cables in Britain are flat (or oval, really) with all the conductors laying side by side.
Here's the 4mm version of T&E (Twin & Earth), with stranded 4mm phase and neutral and a solid 2.5 bare earth wire:
Here's a 3-core-plus-earth, with solid 1.5mm wires (bare earth is 1.0):
[This message has been edited by pauluk (edited 10-19-2003).]