I think (only think) that Hedychium gardnerianum can be planted in the ground it is the Hardiest of the Hedychiums. It would have to be your sunniest dryest spot. If I were going to plant it outside I would take a cutting to be on the safe side.

Surreylad and Meanie would have a better knowledge.

I got the following from the Springwood Nursery Site:

"The foliage and flowering height are the same at around 1.4m, the only difference is the flower colour as both have a superb fragrance. This form has more coronarium influence flower with a paler lemon yellow colored petal and paler yellow orange filament. Slightly later flowering than the St Martins hybrid, if given winter protection under cold glass in large patio containers or green house boarder, it can flower from the beginning of August. Suitable for full sun or shade in a sheltered permanent planting, or if kept under glass in the summer it will require some shade. It is hardy to around -10oc (USDA Zone 8) and extremely wind tolerant, this form has also been called "Devon Cream", (Limited availability)."

Tougher than I thought.

Thanks for the information Pimpernel, as its quite a large plant it would probably be best if I divide it after flowering and put one in the ground and keep a back-up in the greenhouse. I'll find a sheltered spot for the outside plant and see how it does over the winter.