These plants are hardy (apart from one or two cultivars) down to about -5 deg. C for short periods. As they've been inside,you will need to harden them off before placing back outside by leaving them outdoors during the day for short periods, extending the time gradually until, preferably on a mild night, they're outside all the time. As you live in Dorset, you could start to harden them off next week, provided we don't have another sudden arctic blast.

oh ok thanks for the advice. Nice webiste have to say thank you

Hi Mavis... welcome to GoY.
I'm nominating this question for GoYpedia Cordylines.

Scroll down to the alphabet at the base of the page and click on letter C, and then you'll see Cordylines. :o)

I unrapped my small red ones to give them an airing yesterday, I bought them last year and they are not hardy.The green fair better in the cold, but I lost a few in the long 2010-2011 winter,one a lovely pink that was in a fleece tent over the washing line(nowhere to bring them inside) and sadly a green that hadnt been covered in 10years! I just love them.Welcome to the site Mavisoncall I only joined in january myself and love it.(:0)