| J&R Waste Removal Ltd | Water & waste | 2026 |
| J&S Fast Food Ltd | Hospitality | 2023 |
| J&T Home Improvements Ltd | Construction | 2025 |
| J'S Electrical (Swindon) Ltd | Construction | 2014 |
| J-Tec Business Consultants Limited | Wholesale & retail | 2022 |
| J. L. Rymes Ltd | Construction | 2010 |
| J.A.E.M. Limited | Administrative & support | 2005 |
| J.C.E Precast Flooring Ltd | Construction | 2017 |
| J.H.P. Farming Limited | Agriculture & fishing | 1992 |
| J.H.Phillips Ltd | Construction | 2025 |
| J.J. LEE (Bath) Limited | Manufacturing | 1985 |
| J.K Autos Swindon Ltd | Wholesale & retail | 2026 |
| J.L.S Transfers Ltd | Transport & logistics | 2023 |
| J.P Decoration PVT Ltd | Other services | 2024 |
| J.R.Mercer Associates Ltd | Professional & scientific | 2012 |
| J16 Trade Centre Ltd | Construction | 2025 |
| J2M2 Fire Ltd | Professional & scientific | 2025 |
| J3S Technologies Ltd | Information & communication | 2021 |
| J3TRAINING Ltd | Information & communication | 2025 |
| J68M Ltd | Professional & scientific | 2026 |
| JA & LU Limited | Health & social care | 2023 |
| JA Events UK Ltd | Professional & scientific | 2025 |
| JA Solutions UK Limited | Other services | 2009 |
| Jaam Restaurants Ltd | Hospitality | 2017 |
| JAB Construction (SW) Ltd | Construction | 2026 |
| JAB Interior Design Limited | Other services | 2007 |
| JAC Project Services Ltd | Professional & scientific | 2018 |
| Jacek Cieslinski Ltd | Construction | 2014 |
| Jack Contractors Ltd | Construction | 2024 |
| Jackal Works Limited | Professional & scientific | 2022 |
| Jackie Kerr Recruitment Limited | Administrative & support | 2003 |
| Jacks Bistro Ltd | Arts & recreation | 2025 |
| Jacks Dining Ltd | Hospitality | 2025 |
| Jackson Zheng Ltd | Information & communication | 2022 |
| Jacksonbcs Limited | Professional & scientific | 2016 |
| Jacob Haulage Ltd. | Transport & logistics | 2022 |
| Jacobs Transport Ltd | Transport & logistics | 2013 |
| Jadar Consultancy Limited | Professional & scientific | 2018 |
| Jade House Calne Limited | Real estate | 2016 |
| Jade Salons UK Ltd | Other services | 2006 |
| Jadeo Services Ltd | Health & social care | 2023 |
| Jado Group Limited | Extraterritorial | 2017 |
| Jafre Limited | Manufacturing | 2000 |
| JAG Associates Limited | Administrative & support | 2025 |
| JAG Haulage Ltd | Transport & logistics | 2016 |
| JAG Holdings Limited | Real estate | 2004 |
| Jaggz Consulting Services Ltd | Professional & scientific | 2025 |
| Jahks Consultancy Limited | Professional & scientific | 2017 |
| JAI S Limited | Professional & scientific | 2015 |
| Jaime Ackroyd Films Limited | Information & communication | 2023 |
| Jaivamsri Ltd | Information & communication | 2024 |
| Jake Marsh Coaching Limited | Other services | 2023 |
| Jalanibusiness Consulting Limited | Health & social care | 2023 |
| JAM Security Solutions Ltd | Administrative & support | 2013 |
| James Baldwin Ltd | Financial services | 2015 |
| James Barber Decorating Limited | Construction | 2015 |
| James Care Services Ltd | Health & social care | 2015 |
| James Dickinson Financial Planning Limited | Financial services | 2020 |
| James French Software Limited | Information & communication | 2000 |
| James Junk Removal Ltd | Water & waste | 2020 |
| James Knight Collectors Car Consultancy Limited | Professional & scientific | 2021 |
| James Property and Renovations Ltd | Real estate | 2024 |
| James Rowbotham Ltd | Information & communication | 2019 |
| Jamesy's TOP2BOTTOM Ltd. | Construction | 2016 |
| Jamie Norris Consultancy Limited | Professional & scientific | 2023 |
| Jamila Organics Ltd | Wholesale & retail | 2019 |
| Jamio Creations Ltd | Extraterritorial | 2023 |
| Jamio Ltd | Extraterritorial | 2023 |
| Jamirilo Limited | Financial services | 2017 |
| Jamjarfree Limited | Real estate | 2018 |
| Jamr Services Ltd | Wholesale & retail | 2026 |
| Jamsin Property Company Ltd | Real estate | 2015 |
| Jandarf Healthcare Limited | Health & social care | 2021 |
| Jane Allison Equestrian Ltd. | Arts & recreation | 2009 |
| Janmar Property Development Limited | Real estate | 2004 |
| Janson's GAS Services Limited | Construction | 2008 |
| Jarra Jappineh Abroad Ltd | Real estate | 2017 |
| Jarren Heating Ltd | Construction | 2019 |
| Jarren Property Limited | Real estate | 2016 |
| Jars Property Ventures Ltd | Real estate | 2025 |
| Jasmine HO Ltd | Other services | 2025 |
| Jason Catering Limited | Hospitality | 2024 |
| Jason Foods Ltd | Hospitality | 2021 |
| Jasreen Transport Services Ltd | Transport & logistics | 2019 |
| Javerline Limited | Real estate | 2003 |
| Jaws Properties Limited | Real estate | 2018 |
| JAY Ambe Limited | Other services | 2023 |
| Jay's Barbers Swindon Ltd | Other services | 2026 |
| Jayden Care Limited | Health & social care | 2025 |
| Jayell Limited | Hospitality | 2021 |
| Jayne Marriner Consultancy Limited | Administrative & support | 2009 |
| Jayrex Properties Ltd | Real estate | 2021 |
| Jay’S Strength in Motion Limited | Arts & recreation | 2024 |
| Jazzabella Holdings Limited | Financial services | 2019 |
| JB & LW Holdings Limited | Wholesale & retail | 2026 |
| JB & SON Transports Limited | Transport & logistics | 2018 |
| JB Bespoke Decorating Ltd | Construction | 2022 |
| JB Drylining and Plastering Ltd | Construction | 2022 |
| JB Farriers Ltd | Other services | 2022 |
| JB Professional Consultancy Ltd | Information & communication | 2015 |