| J&Jo Builders Ltd | Construction | 2022 |
| J&K Electricals Security Ltd | Administrative & support | 2025 |
| J&K Partners Limited | Wholesale & retail | 1971 |
| J&S Maintenance & Construction Limited | Construction | 2017 |
| J&U Hilife Tech Solutions Ltd | Wholesale & retail | 2026 |
| J'Delle Fragrances Ltd | Manufacturing | 2021 |
| J-Shalom Limited | Extraterritorial | 2003 |
| J. Browne Holdings Limited | Construction | 1975 |
| J. P. G. Builder and Contractors Limited | Construction | 2018 |
| J.A.K Healthcare Ltd | Administrative & support | 2024 |
| J.B. Properties (UK) Limited | Real estate | 2003 |
| J.B. Worldwide Limited | Real estate | 2003 |
| J.B.Shakespeare,Limited | Other services | 1931 |
| J.C. Total Solutions Limited | Other services | 2019 |
| J.E Events Ltd | Other services | 2025 |
| J.G Property Maintenance Services Ltd | Construction | 2019 |
| J.K.Hastings Ltd | Professional & scientific | 2015 |
| J.O.C. Properties Limited | Other services | 1995 |
| J.Ocansey Limited | Health & social care | 2004 |
| J.S.M. Joinery Limited | Manufacturing | 1973 |
| J.T.Smith & SON Pharma Limited | Wholesale & retail | 2007 |
| J.W Real UK Ltd | Wholesale & retail | 2019 |
| J1NURS Ltd | Health & social care | 2021 |
| JA Chicken HUT Ltd | Hospitality | 2023 |
| JA Holdings Private Limited | Real estate | 2026 |
| Jaai Community Healthcare&International Skill Development Training Centre Ltd | Wholesale & retail | 2020 |
| Jaayessentials Group Ltd | Real estate | 2017 |
| Jaba Health Care Services Ltd | Health & social care | 2014 |
| Jabo Holdings Limited | Financial services | 2026 |
| Jabrx Studio Ltd | Information & communication | 2025 |
| Jacey Estates Limited | Real estate | 2015 |
| Jack Bidco Limited | Financial services | 2021 |
| Jack Midco Limited | Financial services | 2021 |
| Jack Topco Limited | Financial services | 2021 |
| Jack's Builders Limited | Construction | 2018 |
| Jackieology Properties Ltd | Households | 2025 |
| Jacksammy Limited | Transport & logistics | 2023 |
| Jackson Ross Steel Limited | Professional & scientific | 2020 |
| Jackson Ross Steel Management Ltd | Real estate | 2024 |
| Jackson Square Residents Association Limited | Households | 1992 |
| Jackson's Electrical Limited | Construction | 2021 |
| Jacota Properties Limited | Real estate | 2017 |
| Jacquie's Kitchen Ltd | Hospitality | 2024 |
| Jadanaomi Ltd | Professional & scientific | 2026 |
| Jade and Alexis Properties Limited | Real estate | 2017 |
| Jade Bidco Limited | Financial services | 2019 |
| Jade MIDCO1 Limited | Financial services | 2019 |
| Jade MIDCO2 Limited | Financial services | 2019 |
| Jade Pikco Limited | Financial services | 2026 |
| Jade Precision Engineering Ltd | Construction | 2012 |
| Jade Tutoring Ltd | Education | 2024 |
| Jade's Office Limited | Administrative & support | 2023 |
| Jadorerileybeauty Ltd | Other services | 2025 |
| Jads Home Ltd | Real estate | 2022 |
| JAE Limited | Extraterritorial | 2023 |
| Jaffnabbq Ltd | Hospitality | 2025 |
| Jaflong Tandoori Ltd | Hospitality | 2022 |
| Jaftim Cars UK Limited | Wholesale & retail | 2023 |
| JAG Electrical Ltd | Construction | 2024 |
| Jagati Consultancy Limited | Administrative & support | 2022 |
| Jagati Limited | Real estate | 2019 |
| Jagdip S Bars & Entertainments Limited | Hospitality | 2022 |
| Jagdish Retail Limited | Wholesale & retail | 2019 |
| Jagfury Ltd | Construction | 2021 |
| Jagg Property Investments Ltd | Real estate | 2024 |
| Jaggo Jewellers Ltd | Manufacturing | 2025 |
| Jagmama Food and Wine Ltd | Wholesale & retail | 2021 |
| Jags Foundation CIC | Education | 2010 |
| Jags Properties Ltd | Real estate | 2017 |
| Jaguar Security Ltd | Professional & scientific | 2018 |
| Jahangir Textile UK Ltd | Wholesale & retail | 2026 |
| Jahjah Citi Ltd | Hospitality | 2025 |
| Jaice Limited | Real estate | 2020 |
| Jainf Traders Ltd | Wholesale & retail | 2025 |
| Jairadhekrishna Ltd | Information & communication | 2019 |
| Jaisal Limited | Wholesale & retail | 2005 |
| Jaisy Tutors Ltd | Education | 2024 |
| Jaiv Accounting Limited | Professional & scientific | 2023 |
| Jaiv Consulting Ltd | Professional & scientific | 2022 |
| Jakmob International (UK) Limited | Transport & logistics | 2012 |
| Jakupovic Holding Limited | Financial services | 2026 |
| JAL Financial and Property Consultants Limited | Real estate | 2018 |
| JAL Support Solutions | Hospitality | 2020 |
| Jalbrins WCS LLP | | 2026 |
| Jalem Cleaning Services Ltd | Administrative & support | 2024 |
| Jalion Group Limited | Real estate | 2025 |
| JAM Data Solutions Ltd | Information & communication | 2022 |
| JAM Project Consulting Ltd | Information & communication | 2023 |
| Jamaat Ahmadiyya Islah Pasand UK Ltd | Other services | 2019 |
| Jamaica Valley Distributors Ltd. | Wholesale & retail | 2016 |
| Jamaka Foods Ltd | Hospitality | 2022 |
| Jamal Ventures Ltd | Professional & scientific | 2026 |
| Jamari Limited | Other services | 2022 |
| Jambo Healthcare Agency Ltd | Health & social care | 2018 |
| James Atkinson Limited | Health & social care | 2012 |
| James Chiltern Limited | Real estate | 2007 |
| James Court (Luton) Limited | Households | 2017 |
| James Court (Pepys Road Wimbledon) Management Company Limited | Real estate | 1984 |
| James Gillam Property Management Ltd | Real estate | 2021 |
| James Locock Pgbm Limited | Construction | 2015 |