| JD Gracie Limited | Administrative & support | 2009 |
| JD Hayes Limited | Real estate | 2016 |
| JD Shisha Limited | Wholesale & retail | 2020 |
| Jd-Architecture Limited | Professional & scientific | 2026 |
| Jdny Van and Driver Hire Ltd | Transport & logistics | 2025 |
| JDV Cloud Solutions Limited | Information & communication | 2025 |
| Jehoiakim Food Store Limited | Wholesale & retail | 2013 |
| JEM Legal Consultancy Limited | Other services | 2012 |
| Jenkins Motors (London) Limited | Wholesale & retail | 2025 |
| Jennifer Singer Education Design Ltd | Professional & scientific | 2011 |
| Jenny Greenwood Counselling Ltd | Health & social care | 2024 |
| Jerry Sync AI Ltd | Information & communication | 2026 |
| Jeston Insurance Brokers Limited | Financial services | 1962 |
| JFB Consultants Limited | Professional & scientific | 2013 |
| JFG Consulting Limited | Professional & scientific | 2010 |
| JFJ Distribution Ltd | Wholesale & retail | 2026 |
| JG Construction Management Limited | Construction | 2008 |
| JHE Management Ltd | Professional & scientific | 2007 |
| JIM Bouley Consulting Ltd | Professional & scientific | 2020 |
| Jinnah Homes Ltd | Real estate | 2024 |
| JJ Delson Ltd | Other services | 2025 |
| JJ Frames Ltd | Financial services | 2023 |
| JJ Plumbing and Drainage Ltd | Construction | 2025 |
| JK (UK) Limited | Construction | 2013 |
| JK AXE Limited | Real estate | 2025 |
| JK Data Ltd | Information & communication | 2019 |
| Jkslfk Properties LLP | | 2023 |
| JLC Projects Limited | Professional & scientific | 2007 |
| JLC Technologies Ltd | Information & communication | 2024 |
| JLF Broadcast Camera Services Ltd | Information & communication | 2023 |
| JLF Finances Ltd | Professional & scientific | 2010 |
| JMD 4 Investments Limited | Real estate | 2016 |
| JMD Alternative Investments Ltd | Real estate | 2024 |
| JMD Group Holdings Investment Ltd | Financial services | 2024 |
| JMD REG Consultancy Limited | Administrative & support | 2017 |
| Jmkd Consulting Limited | Information & communication | 2012 |
| JMV Development (UK) Ltd | Real estate | 2013 |
| JNK Ventures Ltd | Construction | 2025 |
| Joanne Court Management Limited | Households | 1993 |
| Joanne Summerfield User Experience Design and Research Limited | Other services | 2018 |
| JOE Clark Limited | Professional & scientific | 2016 |
| JOE Macklin Ltd | Information & communication | 2020 |
| JOE9T Ltd | Professional & scientific | 2016 |
| Joe’S Pilates & Juice Ltd | Education | 2023 |
| John Parfitt Nuclear Consultancy Limited | Professional & scientific | 1994 |
| Jointing Works Ltd | Construction | 2025 |
| Joma Commercial Limited | Administrative & support | 2021 |
| JON Parker Legal Ltd | Administrative & support | 2022 |
| JON Warden Ltd | Professional & scientific | 2018 |
| Jonas the Plumber Ltd | Construction | 2023 |
| Jonathan Dennis Ltd | Information & communication | 2015 |
| Jonec Investments Limited | Financial services | 2019 |
| Jones Allen Limited | Professional & scientific | 2019 |
| Jones Installations Ltd | Construction | 2016 |
| Jono Mercer Racing Limited | Wholesale & retail | 2021 |
| Jordan's Car Storage Limited | Transport & logistics | 2008 |
| Jordans Mews Management Limited | Households | 1995 |
| Josan Properties Limited | Real estate | 2022 |
| Joss Joss Trading Limited | Wholesale & retail | 2008 |
| Jotender Limited | Extraterritorial | 2015 |
| Journey Songs Limited | Arts & recreation | 1990 |
| Journzie Ltd | Other services | 2022 |
| Jovek Limited | Wholesale & retail | 2018 |
| Jovue Consulting Limited | Professional & scientific | 2019 |
| Joy Hair by MK Ltd | Other services | 2023 |
| Joynest Investments Ltd | Real estate | 2025 |
| JP Man&Van Ltd. | Transport & logistics | 2017 |
| JPC Brickwork Specialist Ltd | Construction | 2025 |
| JR Resources Ltd | Administrative & support | 2020 |
| Jrgordon Electrical Ltd | Construction | 2019 |
| JRH Ltd | Wholesale & retail | 2025 |
| Jrma Services Limited | Professional & scientific | 2025 |
| JTC Trading (UK) Limited | Wholesale & retail | 2015 |
| JTJ Consultancy Ltd | Administrative & support | 2017 |
| JU Richmond T Pizza Ltd | Hospitality | 2022 |
| Jumato Limited | Financial services | 2020 |
| June Services Limited | Information & communication | 2024 |
| Juriansz Properties Limited | Real estate | 2011 |
| Just Call Holly Limited | Administrative & support | 2021 |
| Just Camps Hounslow Ltd | Health & social care | 2025 |
| Just JAM Ltd | Other services | 2018 |
| Justonefix Ltd | Wholesale & retail | 2016 |
| JV Effects Ltd | Information & communication | 2014 |
| JV Hill Limited | Wholesale & retail | 2024 |
| JVB Design Ltd | Professional & scientific | 2023 |
| Jwhitwell Ltd | Professional & scientific | 2025 |
| Jwle Ltd | Construction | 2026 |
| K & B Plumbing-Gas Ltd. | Construction | 2016 |
| K & S LEE Legal Services Ltd | Other services | 2025 |
| K a Recording Limited | Information & communication | 2015 |
| K L Food & Wine Ltd | Wholesale & retail | 2015 |
| K Malvisi Limited | Professional & scientific | 2010 |
| K Singh Property Limited | Real estate | 2025 |
| K W Analytics Ltd | Professional & scientific | 2018 |
| K&G Boath Limited | Health & social care | 2010 |
| K.R. Capital Limited | Real estate | 1995 |
| Kaam Superstore Ltd | Wholesale & retail | 2024 |
| Kaikoura Consulting Limited | Real estate | 2021 |
| Kaizen Construction Ltd | Construction | 2023 |
| Kale Developments Ltd | Real estate | 2024 |