| J E Chapman Ltd | Wholesale & retail | 2025 |
| J F Brickwork & Building Services Limited | Construction | 2018 |
| J F Carpentry Limited | Construction | 2016 |
| J F J Solutions Ltd | Information & communication | 2023 |
| J G Autos Limited | Wholesale & retail | 2001 |
| J Gordon Forestry & Arboriculture Ltd | Agriculture & fishing | 2018 |
| J H Automotive Engineering Limited | Manufacturing | 2018 |
| J H L Enterprises Ltd | Real estate | 2024 |
| J H Plumbing Services Limited | Construction | 2016 |
| J Hancock Consulting Limited | Professional & scientific | 2011 |
| J Igoe Limited | Construction | 2023 |
| J K Pharmacy Solutions Limited | Health & social care | 2009 |
| J Koshy Limited | Information & communication | 2022 |
| J L & M Properties Ltd | Construction | 2024 |
| J Lining Ltd | Construction | 2023 |
| J M E Scaffolding Southern Ltd | Construction | 2024 |
| J P 1 Ltd | Construction | 2022 |
| J P Tattoos Limited | Arts & recreation | 2021 |
| J P Tattoos Southern Ltd | Arts & recreation | 2024 |
| J R S Rail Limited | Transport & logistics | 2013 |
| J R S Signage & Graphics Ltd | Manufacturing | 2025 |
| J Robb Property Ltd | Real estate | 2025 |
| J S Fibretech Limited | Construction | 2021 |
| J S Installations & General Works Limited | Transport & logistics | 2022 |
| J S Smith Consultancy Ltd. | Information & communication | 2014 |
| J S Watches Ltd | Wholesale & retail | 2022 |
| J Towle Consulting Ltd | Administrative & support | 2023 |
| J W Civils Limited | Construction | 2016 |
| J&C Dwellings Ltd | Real estate | 2020 |
| J&J Clark Roofing Ltd | Construction | 2024 |
| J. Archer Powder Coating Ltd | Administrative & support | 2017 |
| J. Ashwell Limited | Construction | 1971 |
| J. Brotherton & Partners Limited | Professional & scientific | 2022 |
| J. Bucknell Ltd | Real estate | 2006 |
| J. Contracting Ltd. | Construction | 2016 |
| J. Johnsey Plumbing & Heating Limited | Construction | 2020 |
| J.C Mills (Southern) Ltd | Construction | 2022 |
| J.C. Parts Limited | Wholesale & retail | 1998 |
| J.E.Morgan Civils Limited | Construction | 2018 |
| J.G Plastering Solutions Ltd | Construction | 2026 |
| J.N Electrical Specialists Limited | Construction | 2023 |
| J.R.I. Technologies Limited | Extraterritorial | 1989 |
| J.Whitney Transport Solutions Ltd | Transport & logistics | 2025 |
| J10 Construction Limited | Construction | 2026 |
| J2 Trading Limited | Financial services | 2005 |
| JA Griffiths Trading Limited | Financial services | 2025 |
| Jaccbel Properties Limited | Real estate | 2001 |
| Jack Fudge Limited | Real estate | 1958 |
| Jack Williams Fitness Ltd | Health & social care | 2020 |
| Jackie YAU Limited | Information & communication | 2014 |
| Jackson Plumbing and Heating Limited | Construction | 2024 |
| Jacs Homes Ltd | Real estate | 2024 |
| Jade Plaice Ltd | Hospitality | 2024 |
| Jade Taussig Limited | Education | 2019 |
| Jah-Femi Entertainment Ltd | Arts & recreation | 2024 |
| Jake Mcardle Coaching Ltd | Education | 2020 |
| Jake Shaw Electrical Ltd | Construction | 2024 |
| Jake Whelan Visuals Ltd | Information & communication | 2025 |
| JAM Financial Solutions Ltd | Financial services | 2015 |
| Jamatt Solutions Ltd | Professional & scientific | 2011 |
| James Clark Ltd | Professional & scientific | 2026 |
| James Field Commercial Limited | Professional & scientific | 2013 |
| James Field Executive Limited | Professional & scientific | 2012 |
| James Fuller Arboriculture Limited | Administrative & support | 2026 |
| James Leckie Construction & Surveying Ltd | Professional & scientific | 2021 |
| James Livingston Automotive Ltd | Professional & scientific | 2024 |
| James Lowe Holdings Ltd | Financial services | 2024 |
| James Moore Heating and Plumbing Limited | Construction | 2020 |
| James Taylor Limited | Real estate | 2017 |
| James Wallace Landscapes and Installations Ltd | Administrative & support | 2026 |
| Jamscones Limited | Information & communication | 2013 |
| Janine Marie London Limited | Other services | 2025 |
| Janpix Investments Ltd | Real estate | 2025 |
| Jarek Property Solutions Ltd | Real estate | 2025 |
| Jasce IT Consulting Limited | Information & communication | 2021 |
| Jasper Rail Limited | Transport & logistics | 2015 |
| Jatote Limited | Real estate | 2021 |
| JAY Properties (Southern) Limited | Construction | 2013 |
| Jayjay Consultancy Limited | Professional & scientific | 2018 |
| Jayz Properties LLP | | 2023 |
| JB Nails Ltd | Other services | 2023 |
| JB Plumbing Heating & Bathrooms Ltd | Construction | 2010 |
| JB Property & Developments Limited | Construction | 2025 |
| JB Signature Valeting & Detailing Ltd | Manufacturing | 2026 |
| JB Site Services Portsmouth Ltd | Construction | 2025 |
| Jbkb Properties Limited | Real estate | 2020 |
| JBM Health Limited | Health & social care | 2015 |
| JBS Fencing Limited | Administrative & support | 2009 |
| JCI Rail Solutions Limited | Transport & logistics | 2013 |
| Jcik Limited | Transport & logistics | 2017 |
| JCP Roofing Ltd | Construction | 2025 |
| JCS Sales Limited | Other services | 2019 |
| JCT 2 Group Ltd | Wholesale & retail | 2025 |
| JD Interior Construction Limited | Construction | 2004 |
| JD Roofing Southern Ltd | Construction | 2022 |
| JD Safety Surveys Ltd | Professional & scientific | 2025 |
| JDB Landscapes Ltd | Administrative & support | 2025 |
| JDE Management Limited | Hospitality | 2010 |
| JDK Heating Limited | Construction | 2014 |
| JDK Marine Ltd | Manufacturing | 2019 |