| J.A.M Cambridge Ltd | Hospitality | 2020 |
| J.D. Rutherford Limited | Agriculture & fishing | 1986 |
| J.F.D. Tech Solutions Ltd | Manufacturing | 2022 |
| J.G.A. Services Ltd. | Real estate | 2008 |
| J.G.E. Limited | Agriculture & fishing | 1997 |
| J.H.Martin & Sons(Littleport)Limited | Administrative & support | 1953 |
| J.I.T. Productions Limited | Arts & recreation | 2008 |
| J.Jose Ltd | Manufacturing | 2025 |
| J.L.B. Electrical Contractor (Cambridge) Ltd | Construction | 2021 |
| J.O. Collective Ltd | Professional & scientific | 2023 |
| J.T.T. Equipment Services Limited | Wholesale & retail | 1982 |
| J.W. Greig Aviation Ltd | Manufacturing | 2019 |
| J.W.Burgess & Sons Limited | Agriculture & fishing | 1954 |
| J3 Enterprises Limited | Financial services | 2025 |
| J56 Estate Management Ltd | Households | 2025 |
| J56 Limited | Construction | 2023 |
| J7 Enterprise Limited | Wholesale & retail | 2012 |
| J7 Group Ltd | Extraterritorial | 2023 |
| J7 Property Ltd | Real estate | 2024 |
| J7 Solutions Ltd | Real estate | 2016 |
| JA Hair Limited | Other services | 2026 |
| JA Renovations Limited | Construction | 2012 |
| Jaan's Golden Granola Ltd | Hospitality | 2013 |
| Jaas Estates Ltd | Real estate | 2025 |
| Jaas Global Trade Ltd | Wholesale & retail | 2025 |
| Jabooh Software Services Ltd. | Information & communication | 2012 |
| Jack 81 Ltd | Manufacturing | 2025 |
| Jack Imp&Exp Co., Ltd | Extraterritorial | 2014 |
| Jack's Gelato Foundation T/A Found C.I.C. | Hospitality | 2025 |
| Jack's Multi-Services & Groundworks Ltd | Construction | 2025 |
| Jackel Aerotech Ltd | Manufacturing | 2024 |
| Jacklin Properties Limited | Real estate | 2016 |
| Jackro Limited | Professional & scientific | 2025 |
| Jacks Gelato Limited | Manufacturing | 2020 |
| Jackson Ritchie Finance Ltd | Manufacturing | 2017 |
| Jada Promo Ltd | Wholesale & retail | 2023 |
| Jade Peach Ltd | Hospitality | 2013 |
| Jade Therapies Limited | Health & social care | 2025 |
| Jadenslion Ltd | Information & communication | 2021 |
| Jafer Ltd | Real estate | 2024 |
| Jafk Limited | Professional & scientific | 2025 |
| Jafl Consulting Limited | Professional & scientific | 2021 |
| JAG Express Limited | Transport & logistics | 2001 |
| Jagex Limited | Information & communication | 2000 |
| Jagnu Aviation Ltd | Manufacturing | 2023 |
| Jagutek Limited | Wholesale & retail | 2008 |
| Jakenzoe Composites Limited | Manufacturing | 2014 |
| Jakins Interiors Limited | Wholesale & retail | 2003 |
| Jakub Sloviak Ltd | Manufacturing | 2025 |
| Jakubík Bluechip Milling Ltd | Manufacturing | 2024 |
| Jalal Stays Ltd | Real estate | 2025 |
| Jama Clothing Ltd | Wholesale & retail | 2021 |
| Jamaica Blue Limited | Hospitality | 2012 |
| Jamal Ahmad Ltd | Real estate | 2025 |
| Jamal LUX Ltd | Hospitality | 2024 |
| Jaman Ltd | Real estate | 2021 |
| Jamco Aviation Ltd | Manufacturing | 2025 |
| James Alexander (Cambridge) Ltd | Construction | 2026 |
| James Baddeley Consulting Limited | Professional & scientific | 2010 |
| James Bradford Motors Limited | Wholesale & retail | 2003 |
| James Brown Management Limited | Other services | 2020 |
| James Challis Building Solutions Ltd | Construction | 2014 |
| James Clarke and Company Limited | Information & communication | 1920 |
| James Dowson Limited | Financial services | 2013 |
| James Fine Wines Limited | Wholesale & retail | 2016 |
| James Keane Racing Limited | Arts & recreation | 2025 |
| James Lynch Consulting Ltd | Information & communication | 2018 |
| James Masih Ltd | Real estate | 2024 |
| James Nurse Close Management Company Limited | Households | 2002 |
| James Ortega Bloodstock Limited | Agriculture & fishing | 2014 |
| James Perera Ltd | Wholesale & retail | 2020 |
| James Pond Licensing Limited | Information & communication | 2018 |
| James Road (Crowland) Management Company Ltd | Households | 2021 |
| James Swift & SON Limited | Manufacturing | 1961 |
| James Tanner Diagnostics Limited | Health & social care | 2020 |
| James-Stokes Holdings Limited | Real estate | 2025 |
| Jamie Piggott Bloodstock Ltd | Agriculture & fishing | 2018 |
| Jamie Spencer Ltd | Arts & recreation | 2014 |
| Jampt Ltd | Financial services | 2025 |
| Jamra Charcoal Grill Ltd | Hospitality | 2020 |
| Jane Dancer Ltd | Professional & scientific | 2019 |
| Jane Designs Limited | Professional & scientific | 2021 |
| Jane Hope Ltd | Professional & scientific | 2019 |
| Jane Rankin Search Limited | Administrative & support | 2013 |
| Jane Sturgess Limited | Health & social care | 2014 |
| Janet Bingham Editorial Limited | Information & communication | 2014 |
| Janeteva Limited | Real estate | 2013 |
| Janjyl Limited | Administrative & support | 2016 |
| Janki Holdings Ltd | Financial services | 2026 |
| Janus Home Systems Ltd | Information & communication | 2003 |
| Janus Publishing Company Limited | Information & communication | 1993 |
| Janus Smart Solutions Ltd | Information & communication | 2020 |
| Janus Technology Limited | Information & communication | 2010 |
| Japan Yezhuang Fertilizer Ltd | Mining & quarrying | 2023 |
| Japan Yoshida Plant Nutrition Co., Ltd | Wholesale & retail | 2023 |
| Japanese Noodle Bar Limited | Hospitality | 2022 |
| JAR Communications Consultancy Ltd | Professional & scientific | 2021 |
| JAR Quality & Regulatory Consultancy Ltd | Professional & scientific | 2016 |
| Jardus Games Ltd | Information & communication | 2025 |
| Jarred Refillery Ltd | Wholesale & retail | 2025 |