| JF Capital Contracting Limited | Professional & scientific | 2014 |
| JF Project Consulting Ltd | Administrative & support | 2016 |
| JFD Secure Limited | Transport & logistics | 2021 |
| Jfjt Limited | Professional & scientific | 2024 |
| Jham Today Ltd | Professional & scientific | 2022 |
| JHG Property Solutions Ltd | Construction | 2020 |
| JIM Davidson Productions Limited | Administrative & support | 2012 |
| JJ Solutions Limited | Professional & scientific | 2023 |
| JJC Props Ltd | Administrative & support | 2026 |
| JJD Hospitality Ltd | Hospitality | 2013 |
| JK Hotels Advisory Limited | Professional & scientific | 2026 |
| JK Paull Limited | Wholesale & retail | 2011 |
| JL Premier Property Limited | Real estate | 2022 |
| JLQ Ltd | Real estate | 2024 |
| JLQ UK Services Ltd | Professional & scientific | 2016 |
| Jmac Business Consulting Limited | Real estate | 2010 |
| Joat London Ltd | Manufacturing | 2011 |
| Jobes Events Ltd | Wholesale & retail | 2021 |
| JOE Loss Limited | Arts & recreation | 1959 |
| Joet Limited | Information & communication | 2025 |
| John Hadley Props Ltd | Construction | 2024 |
| John Martin Homes Limited | Real estate | 2009 |
| John Milsom (Properties) Limited | Construction | 1977 |
| John Simmons & Company Limited | Construction | 1980 |
| Johnsen & Jorgensen Limited | Water & waste | 1980 |
| Johnson Plant Hire Limited | Administrative & support | 2009 |
| JON Stapleton Limited | Information & communication | 2014 |
| Jonathan Adams Law Ltd | Administrative & support | 2019 |
| Jonathan Barnham Design Ltd | Professional & scientific | 2007 |
| Joseph Harry Limited | Administrative & support | 2012 |
| Joshua Eyre Limited | Professional & scientific | 2019 |
| Joy Care Service Limited | Professional & scientific | 2016 |
| Joy Farms Ltd | Administrative & support | 2011 |
| JP Design and Associates Ltd | Professional & scientific | 2018 |
| JP Design Contracts and Agreements Limited | Professional & scientific | 2022 |
| JP Electrical West London Limited | Construction | 2026 |
| JP New Build and Developments Limited | Construction | 2019 |
| JR Media Limited | Information & communication | 2020 |
| JRA Impact Consulting Limited | Professional & scientific | 2025 |
| JRR Cheam Ltd | Real estate | 2015 |
| JSA Legal Ltd | Professional & scientific | 2023 |
| JSI Design Ltd. | Professional & scientific | 2012 |
| JSL London Limited | Hospitality | 2014 |
| JTB Homecare Ltd | Health & social care | 2026 |
| JTW Consulting Limited | Professional & scientific | 2022 |
| Jude Ower Ltd | Professional & scientific | 2019 |
| Jukebox Showroom Limited | Arts & recreation | 2000 |
| Julia Maxwell Limited | Financial services | 2012 |
| July Fourteen Limited | Professional & scientific | 2019 |
| JUM Mechanical Services Ltd | Wholesale & retail | 2024 |
| Jupiter Lithium Limited | Mining & quarrying | 2023 |
| Just Accomadation LLP | | 2019 |
| Just Accommodation Limited | Real estate | 2019 |
| Just Dogs Grooming Limited | Other services | 2022 |
| Just Laptops Ltd. | Wholesale & retail | 2005 |
| Just Paving Limited | Construction | 2025 |
| Jwsl Consulting Ltd | Professional & scientific | 2019 |
| K Burt Consulting Limited | Professional & scientific | 2019 |
| K D ODD Limited | Hospitality | 2006 |
| K P Trading Ltd | Hospitality | 2021 |
| K&P Partnership Limited | Real estate | 2022 |
| K2ISLAND Ltd | Financial services | 2024 |
| K33 Ventures Holding Ltd | Financial services | 2023 |
| Kadium Limited | Information & communication | 1994 |
| Kahu Services Ltd | Professional & scientific | 2025 |
| Kaisi Group Ltd | Extraterritorial | 2015 |
| Kaitech Limited | Construction | 2014 |
| Kalimak Limited | Hospitality | 2025 |
| KAN Homes Ltd | Real estate | 2021 |
| KAN Homes Properties Ltd | Real estate | 2024 |
| Kandy Build and Construction Ltd. | Construction | 2019 |
| Kappa Vita Healthcare Ltd | Health & social care | 2020 |
| Karamya Components Limited | Administrative & support | 2014 |
| Karinya Properties Ltd | Real estate | 2023 |
| Karl Loynton Limited | Administrative & support | 2003 |
| Katies Rental Limited | Real estate | 2021 |
| Kattseyes Limited | Information & communication | 2011 |
| Katy Eatenton Limited | Professional & scientific | 2025 |
| Kavanagh Communications Limited | Professional & scientific | 1998 |
| Kawaii Creations Ltd | Wholesale & retail | 2020 |
| Kay's Watch Shop Limited | Wholesale & retail | 2010 |
| KBA Limited | Administrative & support | 1993 |
| KCS of Surrey Limited | Wholesale & retail | 1998 |
| Kebbi Mining Ltd | Financial services | 2021 |
| Kebe Studio Ltd | Manufacturing | 2025 |
| Keep Calm and Carry on Limited | Wholesale & retail | 2009 |
| Keith Cohen Limited | Health & social care | 2008 |
| Keith Harrington Ltd | Professional & scientific | 2024 |
| Keith Wilson Process Consulting Limited | Professional & scientific | 2019 |
| Kells Solar PV Ltd | Energy | 2014 |
| Kenneth Green Associates Limited | Wholesale & retail | 1992 |
| Kenneth Green Properties Limited | Professional & scientific | 2001 |
| Kensington Construction and Renovation Limited | Construction | 2021 |
| Kenwise Investments Limited | Other services | 2025 |
| Kenwise Limited | Real estate | 1994 |
| Kenwood Park Residents Association Limited | Households | 1982 |
| Keramika Two Limited | Manufacturing | 2019 |
| Kestrel House Holdings Ltd | Financial services | 2019 |
| Kestrel Networks Ltd | Other services | 2011 |
| Kevin F Gangar Limited | Health & social care | 2013 |