| James Sporting Group Ltd | Arts & recreation | 2020 |
| James Tancock Ltd | Construction | 2019 |
| James Taylor and Partners Limited | Health & social care | 2009 |
| James Taylor Flowers Limited | Wholesale & retail | 2025 |
| James Vincent Enterprises Ltd | Information & communication | 2024 |
| James Webb IT Services Limited | Information & communication | 2018 |
| James Wilkins Inspired Creations Ltd | Hospitality | 2009 |
| James Wilmott Limited | Construction | 2014 |
| Jamesb Services Ltd | Other services | 2018 |
| Jamesrichardevents Ltd | Administrative & support | 2025 |
| Jamie & Sons Ltd | Households | 2025 |
| Jamie Clarke Type Ltd | Professional & scientific | 2022 |
| Jamie Cundy Golf Limited | Arts & recreation | 2021 |
| Jamie Feel Great Limited | Administrative & support | 2022 |
| Jamie Innes Limited | Administrative & support | 2022 |
| Jamie Sanigar Promotions Limited | Arts & recreation | 2014 |
| Jamie Ward Limited | Construction | 2025 |
| Jamie Woodman Limited | Real estate | 2019 |
| Jamie's Meat Limited | Wholesale & retail | 2018 |
| Jamies Hair Limited | Other services | 2012 |
| Jamieson Auto Engineers Ltd | Wholesale & retail | 2009 |
| Jamieson Funeral Directors Ltd | Extraterritorial | 2023 |
| Jamieson Projects Limited | Professional & scientific | 2017 |
| Jamike Limited | Real estate | 2014 |
| Jamjar Print Ltd | Manufacturing | 1999 |
| Jamm CK Limited | Manufacturing | 2012 |
| Jammy Custard Studios Ltd. | Professional & scientific | 2011 |
| Jamoose Limited | Professional & scientific | 2023 |
| Jampak Limited | Wholesale & retail | 2019 |
| Jamuna Food & Wine Ltd | Wholesale & retail | 2026 |
| Jamy Investments Limited | Administrative & support | 2004 |
| JAN Anaesthetics Ltd | Health & social care | 2018 |
| JAN Keddy Consulting Ltd | Professional & scientific | 2022 |
| Jane Boston Coaching Ltd | Professional & scientific | 2022 |
| Jane Bridgeman Music Limited | Information & communication | 2003 |
| Jane Clayton & Company Retail Limited | Wholesale & retail | 2015 |
| Jane Cummings Ltd | Professional & scientific | 2019 |
| Jane Evans Trauma Parenting & Behaviour Consultancy Ltd | Professional & scientific | 2015 |
| Jane Keep Limited | Professional & scientific | 2015 |
| Janes Cleaning Services South West Limited | Other services | 2010 |
| Janet Ilieva Education Consultancy Ltd | Professional & scientific | 2014 |
| Janga Film Ltd | Information & communication | 2025 |
| Janic Properties Limited | Real estate | 2018 |
| Janice Cook Limited | Administrative & support | 2017 |
| Janidarr Care Ltd | Health & social care | 2023 |
| Janish Construction Ltd | Construction | 2025 |
| Janora Technologies Ltd | Wholesale & retail | 2025 |
| Janus Coaching Ltd | Education | 2023 |
| Janus Evolution Ltd | Information & communication | 2020 |
| JAO Property Holding Company Ltd | Real estate | 2025 |
| Jaokos Limited | Health & social care | 2013 |
| Japa Travel Ltd | Administrative & support | 2024 |
| Japan Autoparts Ltd | Other services | 2023 |
| Japan United Ltd | Hospitality | 2019 |
| Japanese Knotweed (Ireland) Ltd | Extraterritorial | 2018 |
| Japchaps Estates Limited | Real estate | 2025 |
| Japonicat Ltd | Wholesale & retail | 2022 |
| Jaraff Kunda Enterprise Limited | Health & social care | 2014 |
| Jarc Scenery Ltd | Construction | 2025 |
| Jared Doughty Limited | Arts & recreation | 2013 |
| Jargo Solution Limited | Wholesale & retail | 2022 |
| Jarju Kunda Care Services Ltd | Health & social care | 2024 |
| Jarl Guthrum Business Services Ltd | Information & communication | 2008 |
| Jarl Trading Ltd | Professional & scientific | 2025 |
| Jarman Accountancy and Consulting Ltd | Professional & scientific | 2011 |
| Jarman Construction Consultancy Ltd | Professional & scientific | 2019 |
| Jarpack Ltd | Administrative & support | 2026 |
| Jarramiela Limited | Health & social care | 2021 |
| Jarrell-Ash (UK) Ltd | Extraterritorial | 2019 |
| Jarrett Brothers Limited | Wholesale & retail | 2002 |
| Jars Restaurant Limited | Hospitality | 2016 |
| Jarvis & Evered Limited | Manufacturing | 1950 |
| Jarvis Williams Limited | Professional & scientific | 1991 |
| JAS Building Services (Bristol) Ltd | Construction | 2017 |
| JAS Networks Ltd | Wholesale & retail | 2026 |
| Jascl Holdings Limited | Professional & scientific | 2025 |
| Jasecd Limited | Information & communication | 2012 |
| Jasil Limited | Financial services | 2023 |
| Jasmark Curtainsider Services Limited | Wholesale & retail | 2003 |
| Jasme Consulting Ltd | Information & communication | 2011 |
| Jasmin Enterprises Limited | Other services | 2010 |
| Jasmin Inns Ltd | Hospitality | 2014 |
| Jasmine Residential Mgmt Limited | Households | 2023 |
| Jasob Investments | Financial services | 2019 |
| Jasoh Limited | Administrative & support | 2007 |
| Jason Baker Design Ltd | Manufacturing | 2011 |
| Jason Bidwell Plumbing Ltd | Construction | 2014 |
| Jason Botha Consulting Limited | Professional & scientific | 2025 |
| Jason Bradley Flooring Limited | Construction | 2009 |
| Jason Doyle Racing Limited | Arts & recreation | 2017 |
| Jason Ingram Photography Limited | Professional & scientific | 2013 |
| Jason Paget Limited | Other services | 2003 |
| Jason Simmons Plumbing & Heating Ltd | Construction | 2020 |
| Jason Transporting Ltd | Administrative & support | 2018 |
| Jason Williams Consultancy Ltd | Professional & scientific | 2022 |
| Jason Woods Limited | Information & communication | 2003 |
| Jasons (South West) Limited | Wholesale & retail | 2015 |
| Jasper Jones Design Limited | Professional & scientific | 2026 |
| Jassal Consulting Ltd | Professional & scientific | 2018 |
| Jassoft Ltd | Information & communication | 2010 |