We recently went to 'Future Gardens' situated in the grounds of 'Butterfly World' near St.Albans. Butterfly World is not yet built so there are Chelsea Flower Show type gardens for you to see as well as one small greenhouse containing some butterflies.
The gardens are excellent and well worth a visit. At the moment, they are doing a 2 for 1 admission deal (£12.50) as I suppose they can't charge full price until Butterfly World is fully up and running.
This appears to be the site for the main butterfly dome, and is currently planted with thousands and thousands of sunflowers. Most of the site, including the entrance drive, has been seeded with a really spectacular display of butterfly-attracting flowers.