| Jane Adams Limited | Wholesale & retail | 1965 |
| Jash Realty Ltd | Real estate | 2022 |
| Jash Ventures Limited | Information & communication | 2016 |
| Jason Bradshaw Interiors Limited | Construction | 2004 |
| Jawset Services Ltd | Construction | 2015 |
| JAX Capital Partners Limited | Professional & scientific | 2023 |
| JAY Raam Limited | Wholesale & retail | 2009 |
| Jazzmore Solutions Ltd | Information & communication | 2003 |
| JB Wealth Limited | Professional & scientific | 2018 |
| Jbtj Ltd | Health & social care | 2018 |
| JBW Commercial Services Ltd | Construction | 2012 |
| JC COX Services Ltd | Information & communication | 2019 |
| JCC Projects Ltd | Construction | 2023 |
| JD Oriental Delicacy Ltd | Hospitality | 2024 |
| JD Pharmacy Limited | Wholesale & retail | 2019 |
| JDC Heating Ltd | Construction | 2018 |
| Jdmvh Limited | Professional & scientific | 2009 |
| Jennings & David Construction Limited | Construction | 2008 |
| Jennings Construction London Limited | Construction | 2018 |
| Jerna Limited | Administrative & support | 2017 |
| Jessops (Holdings) Limited | Construction | 2015 |
| Jessops Construction Limited | Construction | 1999 |
| Jessops Developments Limited | Construction | 2017 |
| JFN Property Holdings Limited | Real estate | 2019 |
| JFW Consultancy Ltd | Professional & scientific | 2024 |
| JGP SET Services Limited | Construction | 2022 |
| JHL5 Consultancy Ltd | Professional & scientific | 2025 |
| Jigsaw Design and Construction Limited | Construction | 2005 |
| Jigsaw Site Services Limited | Construction | 2021 |
| Jigsaw Special Projects Limited | Construction | 2020 |
| JJ Capital Investments Ltd | Real estate | 2015 |
| JJ Global Traders Ltd | Wholesale & retail | 2024 |
| JJ Waste and Demolition Services Ltd | Water & waste | 2014 |
| Jjam Investments Ltd | Real estate | 2016 |
| Jjam Topco Limited | Financial services | 2024 |
| Jjambu Ltd | Real estate | 2022 |
| Jjhomeimprovements Ltd | Construction | 2025 |
| JJW Demolition Contractors Ltd | Water & waste | 2025 |
| JKL Property Management Ltd | Real estate | 2015 |
| Jkms Limited | Real estate | 2019 |
| JLH Payroll Services Limited | Administrative & support | 2008 |
| JLM Media Solutions Ltd | Information & communication | 2024 |
| JM Specialist Services Ltd | Energy | 2011 |
| JMB Construction Ltd | Construction | 1998 |
| JMB Surveying Limited | Professional & scientific | 2015 |
| JMD UK Properties Ltd | Real estate | 2020 |
| JMS People Consulting Limited | Professional & scientific | 2026 |
| JMW Residential Limited | Real estate | 2025 |
| Jnts Investments Limited | Real estate | 2018 |
| John Kingsfield Limited | Real estate | 1947 |
| John O'Connor Driving Limited | Education | 1999 |
| John Roberts & Co Lettings Limited | Real estate | 2012 |
| Johnnyrides Ltd | Transport & logistics | 2022 |
| Johnson & Rose Developments Ltd | Construction | 2017 |
| Johnson Group Limited | Real estate | 1990 |
| Johnston Electrical (Design and Installation) Ltd | Construction | 2025 |
| Jois Holdings Ltd | Financial services | 2026 |
| Jojo Books Limited | Information & communication | 2021 |
| Jojo Homes Holdings Limited | Real estate | 2018 |
| Jojo Homes Limited | Real estate | 2019 |
| Jolly Tanning Ltd | Other services | 2021 |
| Josie Pledge Limited | Administrative & support | 2012 |
| Jovans Properties Limited | Real estate | 2016 |
| JPK Financial Limited | Financial services | 2021 |
| Jpld Properties Limited | Real estate | 2019 |
| JPR Investments Limited | Real estate | 2016 |
| JPW Architecture Ltd | Professional & scientific | 2015 |
| JR Building & Development Limited | Construction | 2012 |
| Jrpm Limited | Households | 2022 |
| JSK Homes Limited | Real estate | 2017 |
| JSV Harsha Ltd | Health & social care | 2025 |
| JT Live Ltd | Arts & recreation | 2022 |
| JT Security Solutions Ltd | Administrative & support | 2015 |
| Judex Consulting Limited | Professional & scientific | 2018 |
| Judy Adam Limited | Professional & scientific | 2010 |
| Juicy Tech Solutions Ltd | Information & communication | 2014 |
| Julian Clark Residential Limited | Real estate | 2021 |
| June Raitt Travel Limited | Administrative & support | 1980 |
| Junk Hunters London Ltd | Water & waste | 2025 |
| Junkapp Ltd | Water & waste | 2024 |
| Jupa Limited | Real estate | 2017 |
| Jupiter Festival Miami Ltd | Administrative & support | 2025 |
| Jupiter Festivals Ltd | Administrative & support | 2025 |
| Just Chloe Ltd | Professional & scientific | 2025 |
| Just Design Services Limited | Construction | 1999 |
| JW Cloud Consulting Ltd | Information & communication | 2021 |
| Jwatts Holdings Ltd | Financial services | 2025 |
| Jwatts Renovations Ltd | Construction | 2025 |
| JWP Groundworks & Civils Ltd | Construction | 2025 |
| K Business Solutions Inc UK Limited | Information & communication | 2025 |
| K H Retail Group Ltd | Administrative & support | 2017 |
| K.L.B Grounds Maintenance Limited | Administrative & support | 2015 |
| K21 Ltd | Wholesale & retail | 2019 |
| K7 Prime Estates Limited | Construction | 2018 |
| Kadal Consulting Ltd | Information & communication | 2012 |
| Kadal Property Services Ltd | Real estate | 2021 |
| Kala Hamilton Limited | Real estate | 2023 |
| Kaleidoscope Social Enterprise Limited | Other services | 2011 |
| Kall Kwik (Titchfield) Limited | Administrative & support | 2009 |
| Kanbi Contemporary Limited | Arts & recreation | 2017 |