No earthakitten - get planting, but don't feel yourself restricted to planting a vine in a greenhouse if you're in the south of England. We have a four year old Reisling (green grape) variety planted against a south facing fence. Last year it generated about 130 small bunches of small but very sweet grapes which were perfectly edible but which we turned into wine. Just keep the area around the roots well manured. If you want to keep the vine in your greenhouse, try and somehow keep the roots outside because they can spread over a large area. I believe there is a very famous old black grapevine at Hampton Court which has entire greenhouse to itself but the roots are planted outside and the border in which it rests is just kept unplanted and manured. If you want to grow big black grapes, a greenhouse will be very suitable.