You're talking about the Temperate House? When I was there about 11 years ago the rhododendrons didn't look very good. Maybe they have renovated.

'Fragrantissimum' is a hybrid rhododendron, whereas RR. veitchianum and scopulorum are wild species. Fragrance in rhododendrons is recessive, when they are crossed it diminishes unless care is taken to retain it.

Hardy rhododendrons with strong floral aromas include R. fortunei and its relations (and some of their hybrids), as well as various deciduous azaleas.

Yup it was the temperate house, the fragrantissimum was almost as strong as the scopulorum but nothing like as strong as the veitchianum, nor was the fragrance quite as refreshing. Went there for the orchid festival only to leave the orchid show a little disappointed at the lack of variety. Temperate house and the palm house on the other hand had a fantastic selection of plants.