| J Bruce and Sons Ltd | Professional & scientific | 2020 |
| J C Gallagher Advisory Limited | Professional & scientific | 2023 |
| J C N Inspection Services Ltd | Administrative & support | 2007 |
| J D Metal Fabrications Ltd | Manufacturing | 2013 |
| J Kettle & SON Limited | Construction | 2024 |
| J Lita Homes Limited | Construction | 2024 |
| J Lita Ltd | Construction | 2019 |
| J M Radford Management Ltd | Real estate | 2017 |
| J Niven Furniture Ltd | Manufacturing | 2025 |
| J P Carpentry Solutions Ltd | Construction | 2015 |
| J P FOX Brickwork Limited | Construction | 2017 |
| J PAO Properties LLP | | 2008 |
| J R Gurpreet Limited | Real estate | 1990 |
| J RAY Roofing Limited | Construction | 2019 |
| J Singh Builders Ltd | Construction | 2018 |
| J Spray Ltd | Manufacturing | 2026 |
| J U Autos UK Ltd | Wholesale & retail | 2019 |
| J&A Family Estates Ltd | Real estate | 2023 |
| J&C Interiors Ltd | Administrative & support | 2013 |
| J&K Services Limited | Wholesale & retail | 2023 |
| J&M&M Ltd | Real estate | 2021 |
| J&P Drylining Limited | Construction | 2023 |
| J&R Roofing & Building Ltd | Construction | 2026 |
| J. PAO & Co (Produce) Limited | Professional & scientific | 1992 |
| J. PAO & Co. Limited | Agriculture & fishing | 1984 |
| J.C.Symondson Ltd | Other services | 2015 |
| J.M Roofing & Building Services Ltd | Construction | 2018 |
| J.R.J Couriers Limited | Transport & logistics | 2016 |
| J.T. Displays (Luton) Limited | Professional & scientific | 1976 |
| J.Z Plumbing & Heating Services Ltd | Construction | 2026 |
| JA Chauffeurs Ltd | Transport & logistics | 2025 |
| JA Property Services Ltd | Real estate | 2020 |
| JA Quality Ltd | Construction | 2020 |
| Jaan Autos Ltd | Wholesale & retail | 2026 |
| Jaanki Ltd | Real estate | 2022 |
| JAB & Co Accountants Limited | Professional & scientific | 2024 |
| Jaccs Coffee Shop Ltd | Hospitality | 2017 |
| Jaccs Metal Fabrications Ltd | Manufacturing | 2013 |
| Jack Palmer Ltd | Other services | 2024 |
| Jacks London Ltd | Wholesale & retail | 2010 |
| Jade River LI Limited | Hospitality | 2019 |
| Jade’S Properties Ltd | Real estate | 2024 |
| JAF Trans Ltd | Transport & logistics | 2021 |
| Jaggs Engineering Ltd | Construction | 2022 |
| Jaguar White Limited | Administrative & support | 2011 |
| Jaison Solicitors Ltd | Professional & scientific | 2020 |
| Jaizany Autos Ltd | Information & communication | 2026 |
| Jakbowlski Limited | Professional & scientific | 2013 |
| Jakim Ltd | Health & social care | 2019 |
| Jalalabad Islamic Culture and Education Centre Limited | Other services | 1995 |
| JAM Events Parties Ltd | Arts & recreation | 2021 |
| JAM Packed Boxes Ltd | Administrative & support | 2011 |
| JAM Vans Ltd | Transport & logistics | 2012 |
| James Bridgewater Bathrooms Limited | Construction | 2016 |
| Jameson Owen Limited | Real estate | 2004 |
| Jamie Paul White Ltd | Manufacturing | 2021 |
| Jane-Agabe Healthcare Services Limited | Health & social care | 2018 |
| Janiper Enterprise Limited | Wholesale & retail | 2023 |
| Janiya Ltd | Wholesale & retail | 2025 |
| Jannath Accommodation Limited | Real estate | 2024 |
| Jardine MC Limited | Professional & scientific | 2018 |
| Jarroxs Investments Limited | Administrative & support | 2017 |
| JAS and RAJ Limited | Real estate | 2023 |
| Jasmine Cottage Datchworth Limited | Extraterritorial | 2017 |
| Jasper Green Limited | Professional & scientific | 2017 |
| Jasss Food and Wine Ltd | Wholesale & retail | 2023 |
| Jathra Portfolio Ltd | Real estate | 2021 |
| Javing Ltd | Information & communication | 2016 |
| Jawbox (Harpenden) Limited | Construction | 2020 |
| JAY Bhavani Food Ltd | Hospitality | 2025 |
| Jaycon Ltd | Professional & scientific | 2021 |
| Jayson London Limited | Transport & logistics | 2024 |
| Jbarbosa Windows Ltd | Administrative & support | 2023 |
| JBS Auto Services Limited | Administrative & support | 2022 |
| JBS United Ltd | Construction | 2018 |
| JC & Joinery Ltd | Manufacturing | 2024 |
| JCA Homes Ltd | Real estate | 2020 |
| JCA Lettings Limited | Real estate | 2015 |
| JCG Property Services Limited | Real estate | 2022 |
| JD Construction 24-7 Ltd | Construction | 2021 |
| JDA Sales Limited | Agriculture & fishing | 2014 |
| JDG Networks Ltd | Information & communication | 2016 |
| JDJ Bachalski Limited | Professional & scientific | 1994 |
| JEC Motion Limited | Real estate | 2024 |
| Jedy Farms Ltd | Hospitality | 2021 |
| Jeet&Sons Ltd | Wholesale & retail | 2026 |
| JEL Poultry Ltd | Professional & scientific | 2019 |
| Jepton Investments Ltd | Financial services | 2019 |
| JEQ Consultancy Ltd | Professional & scientific | 2024 |
| Jessell Fire Protection Ltd | Professional & scientific | 2023 |
| JFB Estates Limited | Real estate | 2020 |
| JFS Legal Ltd | Professional & scientific | 2022 |
| JG BSC Limited | Professional & scientific | 2005 |
| JGA Recruitment Group Ltd | Administrative & support | 2006 |
| JGA Ventures Limited | Administrative & support | 2023 |
| JGS Brickwork Ltd | Construction | 2017 |
| JHJ Transport Limited | Transport & logistics | 2024 |
| Jigsaw Holdings Limited | Hospitality | 2025 |
| Jimliz Limited | Wholesale & retail | 2026 |
| Jinfo Limited | Information & communication | 1999 |