You may need two types of connector as the earth strand can be narrower. So 2.5mm blue crimp for live and neutral, 1.5mm red crimp for earth. Buy a few spare and a length of twin and earth to practice on. You may well also need some yellow and green sleeve for the earth wire inside the back box.
Yup, "butt connectors" are the ones for you. You'll need the proper ratchet crimping tool ( http://www.tlc-direct.co.uk/Products/DVDHCR15.html) but the joints will be really strong.
You may need two types of connector as the earth strand can be narrower. So 2.5mm blue crimp for live and neutral, 1.5mm red crimp for earth. Buy a few spare and a length of twin and earth to practice on. You may well also need some yellow and green sleeve for the earth wire inside the back box.