Possible Clues:

• Spiny shrub with clusters of yellow or white flowers
• Article about Langley people in plant
• Archaic lilac occasionally produces bush
• Tree initially as charming as collection in arboretum
• Plant Bill in a secret agency
• Mid-'90s Imogen Heap band
• A chartered accountant spies a shrub
• One with roots in California a US agency arrests
• Wattle tree or shrub
• Caught between teetotallers and half of them coming back in 20 down from the garden centre