It can be done. I've got 3 Afghani clones growing outside at the moment. They were rooted indoors and then moved outside. They're about 1 foot tall and pretty bushy. I've grown it outside a couple of times and it's best to have a mini greenhouse or some make-shift cover to keep the rain off. It takes until well into October before the plants are mature and you know what the UK weather is like in October so you may want to consider a greenhouse. You can get the mini plastic ones from Argos for about £30 - £40.