From the GB Non-Native Species Secretariat:

The term ‘non-native species’ is used throughout this website and is the equivalent of ‘alien’species’ as used by the Convention on Biological Diversity (CBD). Invasive non-native species (the equivalent of invasive alien species or IAS) are broadly defined as species whose introduction and/or spread threaten biological diversity. Non-native species covered by this website include all fauna and flora with the exception of genetically modified organisms (GMOs), bacteria and viruses. Non-native species also refers to species native to Great Britain but outside of their normal range.

Here’s a list of fact files available on the GB NNS site:
http://www.nonnativespecies.org/01_Fact_File/06_Old_Fact_Sheets/

Species include a plethora of water weeds, algaes, mollusks, (mostly transported in  water ballast), and  escapees from the agribusiness, pet and fur trades.