| J P C (UK) Limited | Information & communication | 2000 |
| J P Kinchella Consultancy Ltd | Construction | 2019 |
| J P Reynolds Limited | Professional & scientific | 2004 |
| J Peak Management Limited | Construction | 2013 |
| J Peart Engineering Limited | Professional & scientific | 2008 |
| J Pines Limited | Wholesale & retail | 2012 |
| J Plus D Restoration Ltd | Construction | 2021 |
| J Quinn Investment Holdings Ltd | Financial services | 2024 |
| J R Singh Ltd | Construction | 2026 |
| J R Williams Ltd | Construction | 2017 |
| J S E Interim Management Ltd | Professional & scientific | 2005 |
| J Saunders Properties Ltd | Construction | 2016 |
| J Sullivan Electrical Limited | Construction | 2016 |
| J Turner Consulting Ltd | Professional & scientific | 2018 |
| J Vito Flooring Ltd | Construction | 2021 |
| J W @ Work Ltd | Health & social care | 2012 |
| J W Commons LLP | | 2011 |
| J W Windows Limited | Construction | 2011 |
| J White Property Ltd | Real estate | 2020 |
| J&B Scaffolding Ltd | Construction | 2023 |
| J&D Autos Ltd | Wholesale & retail | 2025 |
| J&D2906 Ltd | Construction | 2019 |
| J&F Cleaner Solutions Ltd | Administrative & support | 2022 |
| J&G Maintenance Services Ltd | Construction | 2025 |
| J&J Fernando Ltd | Real estate | 2024 |
| J&J Saward Properties LLP | | 2024 |
| J&K 16 Ltd | Professional & scientific | 2024 |
| J&K Global Food Ltd | Wholesale & retail | 2020 |
| J&K Investment Properties Ltd | Real estate | 2022 |
| J&N Management Ltd | Professional & scientific | 2017 |
| J&P Food UK Ltd | Hospitality | 2020 |
| J&R UK Properties Ltd | Hospitality | 2025 |
| J&Ru Properties Ltd | Real estate | 2018 |
| J&S Consulting Services Limited | Information & communication | 2024 |
| J&S International Limited | Information & communication | 2023 |
| J&S Mechanical Ltd | Construction | 2020 |
| J'S Exquisites Limited | Health & social care | 2016 |
| J. & S. Welding Services Limited | Construction | 2004 |
| J. Feehily Engineering Limited | Professional & scientific | 2024 |
| J. Fitch Flooring Limited | Construction | 1992 |
| J. Shanahan Conversions Limited | Real estate | 1973 |
| J.& R.Harding Limited | Professional & scientific | 1961 |
| J.A. Huckins Limited | Construction | 1997 |
| J.A.Coles(Removal Contractors)Limited | Transport & logistics | 1969 |
| J.D. Ferrari Ltd | Construction | 2017 |
| J.I Hospitality Limited | Real estate | 2025 |
| J.J. Sweeney Holdings Limited | Financial services | 2023 |
| J.J. Sweeney Limited | Construction | 1996 |
| J.P. Construction Industries & Management Ltd | Professional & scientific | 2026 |
| J.P.B Restorations Limited | Administrative & support | 2025 |
| J.S.F & Sons Ltd | Construction | 2024 |
| J.S.F.Construction Ltd | Construction | 2014 |
| Jaani Ecom Ltd | Wholesale & retail | 2024 |
| Jabbal Holdings Limited | Financial services | 2012 |
| Jabbey Options Ltd | Information & communication | 2025 |
| Jabuticaba Management Limited | Construction | 2025 |
| JAC CAB Hire Ltd | Transport & logistics | 2015 |
| JAC Cars Ltd. | Wholesale & retail | 2017 |
| JAC G Ltd | Households | 2021 |
| JAC9 Ltd | Construction | 2026 |
| Jack Logos and Designs Ltd | Manufacturing | 2015 |
| Jack Movie Ltd | Information & communication | 2015 |
| Jack Union Ltd | Information & communication | 2025 |
| Jackdaw Associates Ltd | Education | 2019 |
| Jacksons Wine Bars Limited | | 1982 |
| Jacksuns of Bexley Ltd | Construction | 2021 |
| Jacob C Brickwork Ltd | Construction | 2026 |
| Jacob's Corner Ltd | Wholesale & retail | 2024 |
| Jacs Projects LLP | | 2007 |
| Jad's Beauties Ltd | Wholesale & retail | 2023 |
| Jade’S Snack Shack Limited | Hospitality | 2024 |
| JAE Ponde Ltd | Construction | 2025 |
| JAE Tools Ltd | Wholesale & retail | 2024 |
| Jaemo Enterprises Ltd | Health & social care | 2015 |
| Jaffa Trading Limited | Transport & logistics | 2016 |
| Jaffary Holdings Limited | Real estate | 2024 |
| Jaffna Young Stars Ltd | Arts & recreation | 2024 |
| JAG Building Services London Limited | Construction | 2013 |
| JAG Property London Ltd | Real estate | 2020 |
| Jagadabhiram Technologies Ltd | Information & communication | 2016 |
| JAI Removal Limited | Transport & logistics | 2026 |
| JAK Care and Recruitment Services Limited | Health & social care | 2023 |
| Jakhu Design and Build Ltd | Construction | 2023 |
| Jaktol Day Centers Ltd | Health & social care | 2020 |
| Jaktol Healthcare Mandatory Training and Recruitment Ltd | Other services | 2013 |
| Jalena Limited | Health & social care | 2014 |
| JAM Property Assets Ltd | Extraterritorial | 2017 |
| JAM Scaffolding Ltd | Construction | 2024 |
| Jamal and Sons Ltd | Construction | 2024 |
| Jamal Services Ltd | Wholesale & retail | 2020 |
| Jamali MED Ltd | Health & social care | 2025 |
| James & Sons Services Ltd | Wholesale & retail | 2026 |
| James Crawford Properties Ltd | Real estate | 2020 |
| James Elias Recruitment Limited | Transport & logistics | 2019 |
| James Green and Nephew Ltd | Wholesale & retail | 2008 |
| James Hennessy Construction Limited | Construction | 1971 |
| James Herbert Brian Celine Limited | Extraterritorial | 2024 |
| James Leonard Electrical Limited | Construction | 2022 |
| James Street Practice Limited | Professional & scientific | 2015 |
| James's Compassionate Care Ltd | Health & social care | 2022 |