Excellent id sheet from the non native species secretariat:
https://secure.fera.defra.gov.uk/nonnativespecies/index.cfm?pageid=135
Hopefully we will have some images here shortly to help with identification, however in the mean time if you have any photos of himalayan balsam, please send them to us
A path with himalayan balsam growing either side. Source: Jeremy Early
Source: Abigail Pedlow/BRERC