Thanks, Andy (though I have now been advised against them - see my other
post).

Whatever method I use, one more question: as I said, I have to extend three
earths, two twisted lives and one single live. Can I run just one single
earth from the three in my connector to the new switch? And can I take just
one single live from the two twisted or should I run both singly and then
twist them again at the new switch? Thanks.