Species Recorded | Taxon | Scientific Name | Common Name | Records | Latest |
| algae or stonewort | Ulva | a sea Lettuce or green laver (unidentified) | 2 | 2015 |
| algae or stonewort | Ulva intestinalis | Gutweed | 6 | 2023 |
| algae or stonewort | Ulva lactuca | Sea Lettuce | 11 | 2017 |
| algae or stonewort | Ulva prolifera | an alga | 1 | 2013 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Urocerus gigas | Greater Horntail Wasp | 10 | 2019 |
| bird | Upupa epops | Hoopoe | 123 | 2021 |
| bird | Uria aalge | Guillemot | 101 | 2022 |
| bug | Unaspis euonymi | a scale insect | 1 | 2022 |
| bug | Uroleucon | a Uroleucon aphid (unidentified) | 2 | 2019 |
| bug | Uroleucon (Uroleucon) cirsii | Large Thistle Aphid | 2 | 2017 |
| bug | Uroleucon (Uromelan) sonchi | a Uroleucon aphid | 1 | 2024 |
| fungus | Unguicularia | an Unguicularia sp. (unidentified) | 1 | 2000 |
| fungus | Urocystis anemones | Anemone Smut | 2 | 2023 |
| fungus | Urocystis magica | a rust | 2 | 2020 |
| fungus | Urocystis violae | Violet Smut | 1 | 1997 |
| fungus | Uromyces appendiculatus | a rust | 1 | 2013 |
| fungus | Uromyces beticola | a rust | 1 | 2007 |
| fungus | Uromyces dactylidis | a rust | 4 | 2020 |
| fungus | Uromyces ficariae | a rust | 3 | 2020 |
| fungus | Uromyces minor | a rust | 1 | 1997 |
| fungus | Uromyces muscari | Bluebell Rust | 6 | 2023 |
| fungus | Uromyces pisi-sativi | a rust | 2 | 2008 |
| fungus | Ustilaginales | a smut or a rust (unidentified) | 1 | 2011 |
| fungus | Ustilago avenae | Loose Smut of Oats & Oat Grass | 6 | 2011 |
| fungus | Ustilago filiformis | a rust | 1 | 1997 |
| fungus | Ustulina | an Ustulina sp. (unidentified) | 2 | 2012 |
| lichen | Usnea | an Usnea sp. (unidentified) | 6 | 2023 |
| lichen | Usnea articulata | a lichen | 1 | 1998 |
| lichen | Usnea cornuta | a lichen | 3 | 2005 |
| lichen | Usnea subfloridana | a lichen | 15 | 2023 |
| mollusc | Unionidae | a freshwater Mussel (unidentified) | 8 | 2023 |
| moss | Ulota | an Ulota sp. (unidentified) | 1 | 2004 |
| moss | Ulota bruchii | Bruch's Pincushion | 39 | 2023 |
| moss | Ulota calvescens | Balding Pincushion | 1 | 2018 |
| moss | Ulota crispa (Hedw.) Brid. sensu Smith (2004) / bruchii agg. | a moss | 11 | 2006 |
| moss | Ulota crispa (sensu Smith (2004)) | Crisped Pincushion | 10 | 2020 |
| moss | Ulota phyllantha | Frizzled Pincushion | 24 | 2023 |
| moth or butterfly - macro moth | Utetheisa pulchella | Crimson Speckled | 1 | 2022 |
| moth or butterfly - micro moth | Udea ferrugalis | Rusty Dot | 906 | 2024 |
| moth or butterfly - micro moth | Udea lutealis | Pale Straw Pearl | 212 | 2024 |
| moth or butterfly - micro moth | Udea olivalis | Olive Pearl | 1343 | 2024 |
| moth or butterfly - micro moth | Udea prunalis | a pyralid moth | 1166 | 2024 |
| moth or butterfly - micro moth | Uresiphita gilvata | Yellow-underwing Pearl | 1 | 1895 |
| plant | Ulex | a gorse (unidentified) | 23 | 2023 |
| plant | Ulex europaeus | Gorse | 1029 | 2024 |
| plant | Ulex gallii | Western Gorse | 149 | 2019 |
| plant | Ulex minor | Dwarf Gorse | 1 | 1982 |
| plant | Ulmus | an elm (unidentified) | 2949 | 2024 |
| plant | Ulmus aggregate | a Plant | 4 | 2007 |
| plant | Ulmus glabra | Wych Elm | 2768 | 2024 |
| plant | Ulmus glabra subsp. glabra | an elm | 1 | 1979 |
| plant | Ulmus glabra x minor = U. x vegeta | Huntingdon Elm | 10 | 2014 |
| plant | Ulmus glabra x minor x plotii = U. x hollandica | an elm | 4 | 2024 |
| plant | Ulmus glabra x plotii = U. ? x elegantissima | a Plant | 1 | 1991 |
| plant | Ulmus minor | a Plant | 29 | 2023 |
| plant | Ulmus minor subsp. minor | Small-leaved Elm | 20 | 2011 |
| plant | Ulmus procera | English Elm | 3953 | 2024 |
| plant | Ulmus sapporo | Sapporo Autumn Gold | 2 | 2016 |
| plant | Umbilicus rupestris | Navelwort | 670 | 2024 |
| plant | Urtica | an Urtica sp. (unidentified) | 6 | 2022 |
| plant | Urtica dioica | Common Nettle | 10129 | 2025 |
| plant | Urtica incisa | a nettle | 4 | 2014 |
| plant | Urtica urens | Small Nettle | 200 | 2023 |
| plant | Utricularia | a bladderwort (unidentified) | 2 | 2004 |
| plant | Utricularia australis | Bladderwort | 1 | 1999 |
| plant | Utricularia minor | Lesser Bladderwort | 1 | 1999 |
| plant | Utricularia vulgaris | Greater Bladderwort | 30 | 2013 |
| plant | Utricularia vulgaris (sens.lat.) | Greater Bladderwort sens.lat. | 5 | 2009 |
| sea-fan, sea anemone or jellyfish | Urticina felina | Dahlia anemone | 7 | 2003 |
| spider | Uloborus plumipes | a spider (Araneae) | 2 | 2022 |
| true fly - cranefly | Ula mollissima | a cranefly | 2 | 2022 |
| true fly - picture-winged, conopid or stilt-legged fly | Urophora cardui | Thistle Gall Fly | 85 | 2024 |
| true fly - picture-winged, conopid or stilt-legged fly | Urophora jaceana | a gall fly | 20 | 2013 |
| true fly - picture-winged, conopid or stilt-legged fly | Urophora quadrifasciata | a gall fly | 10 | 2013 |
| true fly - picture-winged, conopid or stilt-legged fly | Urophora solstitialis | a gall fly | 1 | 1988 |
| true fly - picture-winged, conopid or stilt-legged fly | Urophora stylata | a gall fly | 11 | 2025 |