| J.C. Rusby Limited | Real estate | 2001 |
| J.E. Ablett & Co. Limited | Construction | 1997 |
| J.E. Oxley (Landscaping) Limited | Other services | 1986 |
| J.E.Stringer Holdings Ltd | Wholesale & retail | 2023 |
| J.F.A.N (Jesus for ALL Nations) Ltd | Other services | 2008 |
| J.G. Squire (Holidays) Limited | Real estate | 1979 |
| J.G. Squire Limited | Wholesale & retail | 1964 |
| J.G.W. Coatings Limited | Manufacturing | 1977 |
| J.H. Milnes Limited | Administrative & support | 1998 |
| J.H.Kingswood Ltd | Construction | 2022 |
| J.H.S. (UK) Limited | Construction | 1985 |
| J.K Matharu Ltd | Other services | 2017 |
| J.K.S. Haulage Limited | Information & communication | 2003 |
| J.Lax Building Ltd | Construction | 2025 |
| J.M. Services (GB) Limited | Real estate | 1997 |
| J.Morley Construction Services Limited | Construction | 2015 |
| J.Newsome (Tools) Limited | Wholesale & retail | 1972 |
| J.O Electrical Design & Installation Ltd | Construction | 2023 |
| J.P. Cooling Services Limited | Manufacturing | 2004 |
| J.P. Portfolio Ltd. | Real estate | 1994 |
| J.S.I. Properties Limited | Real estate | 2002 |
| J.S.O Environmental Ltd | Professional & scientific | 2026 |
| J.S.O Fire Consultants Ltd | Professional & scientific | 2023 |
| J.S.O Talent Ltd | Administrative & support | 2024 |
| J.Sammans Limited | Wholesale & retail | 2025 |
| J.T. Carpet Fitting Services Ltd | Construction | 2018 |
| J.T.Barker & Sons,Limited | Manufacturing | 1943 |
| J.T.Hatched Ltd | Wholesale & retail | 2016 |
| J.W. Young (Butchers) Limited | Wholesale & retail | 1978 |
| J.Youle and Company Limited | Manufacturing | 1912 |
| J3NGO'S Ltd | Wholesale & retail | 2023 |
| J4WCT Ltd | Professional & scientific | 2025 |
| JA Automobiles Limited | Wholesale & retail | 2023 |
| JA Dixon Consultants Ltd | Professional & scientific | 2020 |
| JA Visuals Ltd | Information & communication | 2021 |
| JAA Healthcare Ltd | Wholesale & retail | 2025 |
| Jaan Lounge Ltd | Hospitality | 2023 |
| Jaancu Trade Limited | Wholesale & retail | 2026 |
| Jaas Editing Limited | Information & communication | 2012 |
| JAB Electrical Wholesale Limited | Wholesale & retail | 2019 |
| JAB Health Limited | Information & communication | 2015 |
| JAB Infection Services Ltd | Health & social care | 2026 |
| JAB Management Limited | Professional & scientific | 2023 |
| JAB Project Management Ltd | Construction | 2025 |
| JAB Property Rental Limited | Real estate | 2024 |
| Jabai Estates Ltd | Real estate | 2006 |
| Jabeerwocky Ltd | Hospitality | 2018 |
| Jabir’S Services Ltd | Professional & scientific | 2025 |
| Jabru Ltd | Hospitality | 2014 |
| Jabula Design Ltd | Professional & scientific | 2014 |
| Jabz Hair Cosmetics Limited | Other services | 2025 |
| JAC Paving & Groundworks Ltd | Construction | 2024 |
| JAC Utilities Ltd | Information & communication | 2025 |
| Jacadams Estates Limited | Real estate | 2026 |
| Jack & Ronnie Limited | Hospitality | 2024 |
| Jack Barton Motion Design Ltd | Professional & scientific | 2025 |
| Jack Customz Limited | Wholesale & retail | 2013 |
| Jack Haigh Coaching Ltd | Education | 2022 |
| Jack O'Brien Limited | Administrative & support | 2026 |
| Jack Parker Ltd | Wholesale & retail | 2020 |
| Jack Scott's Services Ltd | Administrative & support | 2025 |
| Jack's Fisheries Limited | Hospitality | 2014 |
| Jack's Foods Limited | Hospitality | 2018 |
| Jack's Sandwich Stop Limited | Hospitality | 2020 |
| Jackal Films Limited | Information & communication | 2025 |
| Jackal Pack Ltd. | Manufacturing | 2017 |
| Jackdor Films Limited | Information & communication | 2007 |
| Jacko's Hand Car Wash Ltd | Wholesale & retail | 2023 |
| Jackson Cleaning Services Limited | Administrative & support | 2005 |
| Jackson DV Properties Ltd | Construction | 2024 |
| Jackson Hospitality Limited | Hospitality | 2023 |
| Jackson Payne Properties Ltd | Real estate | 2019 |
| Jackson Silver Limited | Arts & recreation | 2012 |
| Jackson Swift Limited | Professional & scientific | 2015 |
| Jackson Woodturners Ltd | Wholesale & retail | 2014 |
| Jackson's Greeting Cards Limited | Wholesale & retail | 1997 |
| Jackson's Travel Ltd | Transport & logistics | 2023 |
| Jacksons the Bakers Limited | Manufacturing | 2002 |
| Jaco Tooling Company Limited | Manufacturing | 1983 |
| Jacob Dylan Limited | Wholesale & retail | 2012 |
| Jacob Perkins Ltd | Construction | 2023 |
| Jacob's Wrought Iron Limited | Manufacturing | 2023 |
| Jacscar LLP | | 2024 |
| Jacviv Limited | Health & social care | 2019 |
| Jadco Limited | | 1984 |
| Jade House 88 Ltd | Hospitality | 2023 |
| Jade Property Management Ltd | Real estate | 2015 |
| Jade Youth & Community Ltd | Other services | 2008 |
| Jadebeam Limited | Hospitality | 2018 |
| Jadeinvestments Ltd | Professional & scientific | 2024 |
| Jadkale Limited | | 1982 |
| JAF Technical Engineering Services Ltd | Professional & scientific | 2024 |
| Jaffer Properties Limited | Real estate | 2004 |
| Jaffora Ltd | Wholesale & retail | 2026 |
| Jaflong Lounge Limited | Hospitality | 2023 |
| JAG Warehousing & Distribution Limited | Transport & logistics | 2013 |
| Jaga Leisure Ltd | Arts & recreation | 2019 |
| Jagaj Choices Ltd | Administrative & support | 2017 |
| Jager Associates Limited | Water & waste | 2003 |
| Jager Nottingham Limited | Administrative & support | 2009 |