| IYE (England) Limited | Wholesale & retail | 1980 |
| IZG Construction Ltd | Construction | 2023 |
| J & a Windows Limited | Construction | 2014 |
| J & C Harlie Limited | Other services | 2017 |
| J & J Interiors (UK) Limited | Construction | 2019 |
| J & J Pro Roofing Services Limited | Construction | 2024 |
| J & JS Electrical Ltd | Construction | 2023 |
| J & K Durasteel Installations Limited | Construction | 2016 |
| J & T Security Solutions Limited | Manufacturing | 2021 |
| J a Andrews Consulting Limited | Administrative & support | 2018 |
| J a Outhwaite Limited | Professional & scientific | 2015 |
| J and J Roofing and Dampness Ltd | Construction | 2025 |
| J B a Kitchens Limited | Construction | 2014 |
| J C Construction Group Ltd | Construction | 2021 |
| J C Metal Recycling Limited | Administrative & support | 2005 |
| J C P International Limited | Transport & logistics | 2008 |
| J C Rail (Kent) Ltd | Other services | 2016 |
| J Collins Property Limited | Real estate | 2012 |
| J D M Security Services Limited | Administrative & support | 2024 |
| J D Systems Limited | Manufacturing | 1993 |
| J Elphinstone Heating & Plumbing Limited | Construction | 2015 |
| J Hearn Properties Limited | Real estate | 2026 |
| J Hinton Consulting Limited | Wholesale & retail | 2012 |
| J J Training Centre Ltd | Education | 2019 |
| J Mason TM Ltd | Construction | 2024 |
| J P Retail Limited | Other services | 2005 |
| J Parmenter Limited | Construction | 2024 |
| J Patterson Ltd | Administrative & support | 2017 |
| J R Couriers Ltd | Transport & logistics | 2018 |
| J Rose Electrical Services Limited | Construction | 2019 |
| J S L Window Cleaning Services Limited | Administrative & support | 2012 |
| J S Land & New Homes Limited | Other services | 2019 |
| J Stewart Heating & Plumbing Limited | Construction | 2019 |
| J W Davis Enterprises Limited | Administrative & support | 2002 |
| J W Press Limited | Manufacturing | 2017 |
| J Walden Interiors Limited | Construction | 2016 |
| J Willoughby Services Limited | Construction | 2026 |
| J Zahra Limited | Other services | 2019 |
| J&A Landscapes Ltd | Administrative & support | 2024 |
| J&A Media Limited | Professional & scientific | 2024 |
| J&J Carpentry and Joinery Ltd | Construction | 2019 |
| J&J's Group Ltd | Professional & scientific | 2026 |
| J&M Capital Ltd | Information & communication | 2018 |
| J&M Care Direct Ltd | Information & communication | 2017 |
| J&M Premier Construct Ltd | Construction | 2024 |
| J&M Thermal Limited | Construction | 2021 |
| J&M Vehicle Repairs Ltd | Wholesale & retail | 2021 |
| J&P Soft Furnishings Limited | Manufacturing | 2018 |
| J-Tech Diagnostics Limited | Manufacturing | 2023 |
| J. Nissi Health Care and Medical Rehabilitation Ltd | Health & social care | 2010 |
| J.A.R Aviation Limited | Professional & scientific | 2018 |
| J.D. Jetwash Ltd | Administrative & support | 2025 |
| J.E.Turner's Properties Limited | Real estate | 1951 |
| J.G Carpentry and Construction Services Limited | Construction | 2022 |
| J.G.Wells Property Limited | Real estate | 2022 |
| J.H. Contractors (Essex) Limited | Construction | 2016 |
| J.I. Case Trustee Limited | Professional & scientific | 2004 |
| J.L. Harrison & SON (Air Conditioning) Limited | Manufacturing | 1961 |
| J.L.C Carpentry & Building Limited | Construction | 2018 |
| J.Lut Holdings Limited | Real estate | 2020 |
| J.N Training & Building Ltd | Education | 2021 |
| J.S Monoflexing Limited | Construction | 2025 |
| J.S. & D.E. Webb (Joinery & Timber Merchants) Limited | | 1975 |
| J.S.F. Cleaning Services Ltd | Administrative & support | 2009 |
| J.Saviation Limited | Manufacturing | 2026 |
| J.Tocsolutions Ltd | Wholesale & retail | 2025 |
| J15 Limited | Health & social care | 2019 |
| J2C Properties Ltd | Real estate | 2021 |
| J3 Property Services Limited | Real estate | 2026 |
| J4 Truck Components Limited | Wholesale & retail | 2013 |
| J42 Limited | Construction | 2015 |
| J8 Mechanical Services Limited | Other services | 2024 |
| JA Global Solutions Limited | Professional & scientific | 2012 |
| JAB Digital Creations Limited | Information & communication | 2024 |
| Jaboc Ltd | Wholesale & retail | 2021 |
| Jacbarn Limited | Information & communication | 2013 |
| Jack & Jason Groundworks Limited | Construction | 2018 |
| Jack Tipper Coaching Limited | Other services | 2022 |
| Jackson Sims Holdings Limited | Other services | 2024 |
| Jackson Sims Recruitment Limited | Administrative & support | 2018 |
| Jackson Sims Recruitment Temporary Limited | Administrative & support | 2021 |
| Jad's Retail Limited | Wholesale & retail | 2018 |
| Jadack Limited | Professional & scientific | 2022 |
| Jaffna Gold Foods Ltd | Hospitality | 2026 |
| JAG Railway Ltd | Construction | 2015 |
| Jaguar Design & Print Ltd. | Manufacturing | 2004 |
| Jait Limited | Information & communication | 2024 |
| JAJ Child Care Ltd | Health & social care | 2024 |
| JAJ Healthcare Solutions Ltd | Health & social care | 2024 |
| Jake Mcarthur Coaching Ltd | Other services | 2021 |
| Jakob Alexander Limited | Other services | 2025 |
| Jalapeno Funding Limited | Financial services | 2019 |
| Jalvi Group Ltd | Wholesale & retail | 2026 |
| JAM Basingstoke Limited | Real estate | 2021 |
| JAM Electrical Supplies Limited | Wholesale & retail | 2004 |
| JAM Exeter Limited | Real estate | 2023 |
| JAM Freehold Ltd | Real estate | 2026 |
| JAM Manor Road Limited | Real estate | 2020 |
| JAM Newmarket Limited | Real estate | 2021 |
| JAM Real Estate Limited | Real estate | 2017 |