| ISO Consultancy Services Ltd | Professional & scientific | 2017 |
| Istanbul Hairstyle Ltd | Other services | 2025 |
| IT Nation Ltd | Wholesale & retail | 2019 |
| It's ALL About Dogs Ltd | Real estate | 2013 |
| ITC Property Development Catcott Limited | Construction | 2024 |
| ITC Property Development Limited | Construction | 1998 |
| Itech (Homes) Limited | Construction | 2017 |
| Ivascular UK Limited | Health & social care | 2023 |
| Ivory Tower Properties Ltd | Real estate | 2022 |
| IW Consultancy Services Ltd | Professional & scientific | 2023 |
| J & K Aquatics Limited | Wholesale & retail | 1985 |
| J & K Barnard (Farms) Limited | Agriculture & fishing | 1997 |
| J & K Cridge Ltd | Real estate | 2025 |
| J & M Products (UK) Ltd | Financial services | 2025 |
| J & V Property Investments Limited | Real estate | 2021 |
| J and S Haulage SW Ltd | Transport & logistics | 2023 |
| J B Woodcraft Limited | Manufacturing | 2022 |
| J Blockbuster Limited | Information & communication | 2017 |
| J D Marquees Limited | Administrative & support | 2020 |
| J E Webber Construction Limited | Construction | 2013 |
| J E Webber Rentals Ltd | Real estate | 2020 |
| J M Civils (SW) Limited | Construction | 2023 |
| J W Kilmartin Limited | Construction | 2008 |
| J Wilson Transport Ltd | Transport & logistics | 2025 |
| J&D PI Limited | Real estate | 2019 |
| J&H Autos Ltd | Wholesale & retail | 2025 |
| J&L Quality Construction Limited | Construction | 2022 |
| J&W Property Solutions Ltd | Real estate | 2025 |
| J. a. Shepherd Construction Limited | Construction | 2008 |
| J.E.C. Property Developments Ltd | Real estate | 2023 |
| J.E.C. Property Group Ltd | Real estate | 2023 |
| J.K. Rolling & Learning Driving School Ltd | Education | 2025 |
| J.Linham & Sons Limited | Manufacturing | 1962 |
| Jaba Spice Limited | Hospitality | 2016 |
| Jackie Landen Ltd | Professional & scientific | 2016 |
| Jackson Electrical Construction Limited | Construction | 2024 |
| Jacob Holdings Limited | Financial services | 2018 |
| Jacob Medical Imaging Ltd | Health & social care | 2019 |
| Jacob Property Holdings Ltd | Real estate | 2020 |
| Jagiri Transport Ltd | Transport & logistics | 2026 |
| JAI Herbert MMA Ltd | Arts & recreation | 2023 |
| JAK Cafe & Laundrette Somerset Ltd | Administrative & support | 2025 |
| James Napper Litter Ltd | Wholesale & retail | 2026 |
| James Taylor Carpentry Contractors Limited | Construction | 2020 |
| James White Sales Success Limited | Other services | 2018 |
| Jasper Personnel Ltd | Administrative & support | 2024 |
| Jasun Envirocare PLC | Manufacturing | 1972 |
| Jasun Filtration Limited | Manufacturing | 2011 |
| Jasun Ltd | Manufacturing | 2020 |
| JAT Homes Ltd | Real estate | 2024 |
| JB Jetting Services Limited | Water & waste | 2020 |
| JB Syrups Ltd | Extraterritorial | 2021 |
| JBL Europe Limited | Real estate | 2001 |
| JC Discovery Ltd | Professional & scientific | 2024 |
| JC Porter Plant Limited | Construction | 2003 |
| JD Conservatory Cleaning Ltd | Administrative & support | 2026 |
| JD Financial Software Solutions Ltd | Information & communication | 2023 |
| JDB Group SW Limited | Construction | 2024 |
| JE Savage Ltd | Professional & scientific | 2018 |
| Jean Kirk Pubs Ltd | Administrative & support | 2016 |
| JES Plumbing & Tiling Ltd. | Water & waste | 2015 |
| Jess Cunningham Consultancy Ltd | Professional & scientific | 2026 |
| Jewn Holdings Ltd | Professional & scientific | 2011 |
| JFE Property Management Ltd | Real estate | 2025 |
| JG Atlas Consultancy Ltd | Information & communication | 2022 |
| JH Valeting Ltd | Administrative & support | 2019 |
| Jheal & Co. Limited | Real estate | 2025 |
| Jheg Holdings Ltd | Construction | 2022 |
| Jigsaw Bag-In-Box Limited | Wholesale & retail | 2004 |
| Jimer Ltd | Professional & scientific | 2018 |
| JJ Process Installation Limited | Manufacturing | 2011 |
| JJF Developments Limited | Construction | 2013 |
| JJL Electrical Solutions Limited | Wholesale & retail | 2016 |
| JKD PUB Management Limited | Hospitality | 2025 |
| JL Aesthetics Limited | Other services | 2026 |
| JL North Dimension Surveys Ltd | Professional & scientific | 2026 |
| Jlch Limited | Health & social care | 2025 |
| JLM Landscaping & Groundworks Ltd | Administrative & support | 2020 |
| JLM Property & Investments Limited | Real estate | 2025 |
| JLR Steadfast Builders Limited | Construction | 2011 |
| JM Surveys Ltd | Professional & scientific | 2019 |
| Joaozinho Elegant Eats Limited | Wholesale & retail | 2025 |
| JOB Solutions Ltd | Other services | 2016 |
| JOE French Plastering Limited | Construction | 2026 |
| JOE Marsh Recording Ltd | Information & communication | 2019 |
| John Anderson Creative Ltd | Professional & scientific | 2020 |
| John Chisholm Consulting Limited | Construction | 2019 |
| John Marchant Electrical Ltd | Construction | 2012 |
| John Papworth Limited | Professional & scientific | 2000 |
| John Rowlands Consultancy Limited | Professional & scientific | 2023 |
| John Waddon (1967) Limited | Manufacturing | 1967 |
| Johnson Metals Ltd | Water & waste | 2005 |
| Johnson Vitality Limited | Wholesale & retail | 2024 |
| Johny Spedition Limited | Transport & logistics | 2026 |
| Jolaw Limited | Health & social care | 2019 |
| Jolly Jumpers Playzone Limited | Arts & recreation | 2015 |
| JON PG Limited | Professional & scientific | 2009 |
| Jonathan Williams UK Limited | Construction | 2007 |
| Jones Bros Decorators Limited | Construction | 2015 |
| Jools Jewellery Ltd | Wholesale & retail | 2011 |