Originally from China, buddleia was introduced to Britain as a garden plant about 1890. Its copious nectar production famously attracts butterflies - more than any native plant species! Some conservation organisations encourage (or used to, before realising its invasive nature) people to plant buddleia to attract butterflies to wildlife gardens. However, while providing nectar for the adults, it provides no food for the leaf-eating caterpillars of most species.
Buddleia is also highly invasive and a threat to native plant diversity. Producing 3 million small wind-blown seeds from a single bush, it colonises bare and disturbed ground especially well, and thrives in dry stony soils with low humus content. Once established buddleia can quickly form dense monospecific stands. While buddleia may actually be a useful wildlife resource on urban waste ground, railway yards etc. which would otherwise be barren, on heathland it is an unwelcome competitor with native plants.
We have some areas in which buddleia is spreading, (particularly near the boundaries where it seeds in from adjoining properties) and some individuals scattered over the plateau which might be the beginnings of dense colonies. The bare gravel areas from which runways and roads have been removed are favourable sites for colonisation. The main concern is that buddleia will invade these areas before more desirable heathland species such as heather become established.