Marine Biological Association  

There is a loose UK network of organisations collecting and communicating data.  A key focus is the UK Defra Non-Native Species Secretariat (NNSS)
Recording Invasive Species Counts (RISC) programme.  In collaboration with the NERC CEH - Centre for Ecology and Hydrology (the Biological Records Centre) - it provides reporting software that gathers information - with links to the National Biodiversity Network.  Species and corresponding organisations collaborating in RISC are: /more.....Animals:

• Muntjac deer - the Mammal Society, The People's Trust for Endangered species,
• Zebra mussel - The Conchological Society,
• Mitten crab - The Marine Biological Association of the UK,
• American bullfrog - Amphibian and Reptile Conservation
• Citrus longhorn beetle - Food and Environment Research Agency
  
• Western conifer seedbug - Terrestrial Heteroptera Recording Scheme for GB and Ireland
  
• Southern green shieldbug - Terrestrial Heteroptera Recording Scheme for GB and Ireland
• Rhododendron leafhopper - Auchenorrhyncha Recording Scheme for GB and Ireland
  
• Signal crayfish - CEH
  

Plants:

• Water primrose - Botanical Society of the British Isles
  
• Tree of heaven - Botanical Society of the British Isles
• American skunk-cabbage - Botanical Society of the British Isles
• Floating pennywort - Botanical Society of the British Isles
• Water fern - Botanical Society of the British Isles
• Wakame - The Marine Biological Association of the UK
• Rhododendron - Botanical Society of the British Isles
• Himalayan balsam  - Botanical Society of the British Isles

And outside the RISC programme, there are other mapping and recording schemes that capture invasive data:

• Grey Squirrel - the Mammal Society
• Ring-necked parakeet - BTO Birdtrack, Project parakeet
• Harlequin ladybird - Harlequin ladybird survey
• Horse Chestnut leaf-miner - Conker Tree Science - a collaboration between the Universities of Bristol and Hull and NERC
  

These are the citizen science/mass observation projects.  There are many more species listed, research project and eradication initiatives listed on the GB Non-Native Species Secretariat site.