| JML Innovation MAX Limited | Real estate | 2024 |
| Jmlt Investments Ltd | Financial services | 2025 |
| Jmnl Trading Limited | Financial services | 2017 |
| JMP Medics Limited | Health & social care | 2012 |
| JN Automotive Ltd | Wholesale & retail | 2024 |
| JNF Drylining Ltd | Construction | 2025 |
| JNF Maintenance Ltd | Construction | 2025 |
| JO Clift Consulting Limited | Professional & scientific | 2019 |
| JOB Hunters London Limited | Construction | 2009 |
| Joe&Dot LLP | | 2024 |
| Joe's Gourmet Foods Limited | Manufacturing | 2010 |
| JOH Productions Limited | Administrative & support | 2022 |
| Johal Investment Group Limited | Real estate | 2022 |
| John Balsom Photography Ltd | Other services | 2013 |
| John H Trayner Consultancy Limited | Professional & scientific | 2024 |
| John S. Miller Limited | Real estate | 1974 |
| Johnglacier Ltd. | Information & communication | 2022 |
| Johnson Knight Properties Limited | Real estate | 2016 |
| Jolina Ltd | Wholesale & retail | 2022 |
| JON Miles Cars Ltd | Wholesale & retail | 2021 |
| Jonas Property Management Ltd | Real estate | 2024 |
| Jonathan Gregory Associates Limited | Professional & scientific | 2008 |
| Jordan Corporation Limited | Real estate | 2018 |
| Jordan Property Rentals Limited | Real estate | 2017 |
| Jordan Woods Group Limited | Wholesale & retail | 2019 |
| Jordan Woods Group Mobiles Ltd | Wholesale & retail | 2026 |
| Jordan Woods Telecoms & IT Limited | Wholesale & retail | 2024 |
| Joseph & Joseph Property Group Limited | Real estate | 2025 |
| Joseph Manton Gunmaker Limited | Extraterritorial | 2019 |
| Josie's Farm Limited | Administrative & support | 2017 |
| JOV Healthcare Limited | Health & social care | 2019 |
| Jozef Investments Limited | Construction | 2025 |
| JPE Ventures Limited | Professional & scientific | 2024 |
| JPK Estates Limited | Other services | 2014 |
| Jpms (2025) Limited | Wholesale & retail | 2025 |
| JPN Public Health Training Ltd | Education | 2019 |
| Jprb Progressive IT Ltd | Information & communication | 2007 |
| Jpss Investments Limited | Real estate | 2023 |
| Jr.Bryant Ltd | Professional & scientific | 2025 |
| JS Design & Consultancy Ltd | Professional & scientific | 2020 |
| JS GAS Heating Ltd | Construction | 2023 |
| JS Lease Limited | Real estate | 2021 |
| JS10 Limited | Administrative & support | 2024 |
| JS20 Property Limited | Real estate | 2021 |
| JSD Properties Ltd | Real estate | 2014 |
| Jsdl Limited | Real estate | 2015 |
| Jsdl Property Limited | Real estate | 2015 |
| JSE Houses Limited | Real estate | 2017 |
| JSE Lettings Limited | Real estate | 2021 |
| JSE Residential Homes Limited | Real estate | 2017 |
| JT Bespoke Estate Agency Limited | Administrative & support | 2014 |
| JT Bespoke Lettings Ltd | Extraterritorial | 1971 |
| JT Shirlin Limited | Administrative & support | 2016 |
| JTL Roofing Services Limited | Construction | 2016 |
| JTN Real Estate & Investments Limited | Real estate | 2024 |
| Jubilee News Limited | Wholesale & retail | 2022 |
| Julia Court Freehold Management Ltd | Households | 2011 |
| Julia Leona Ltd | Manufacturing | 2019 |
| Julian-Build UK Limited | Construction | 2018 |
| Junai Import and Export Ltd | Wholesale & retail | 2025 |
| Junction Sweets Limited | Wholesale & retail | 2010 |
| Jungo Limited | Information & communication | 2026 |
| Junksaway Ltd | Water & waste | 2025 |
| Juno Pets Ltd | Wholesale & retail | 2024 |
| Just a Perfect Day Limited | Administrative & support | 2019 |
| Just Fire Safety Limited | Wholesale & retail | 2017 |
| Just JO Limited | Professional & scientific | 2007 |
| Just Pallet Wrap Ltd | Other services | 2021 |
| Just Rocks! Limited | Wholesale & retail | 2009 |
| Justso Comms Limited | Other services | 2020 |
| JVM Logistics and Sales Limited | Wholesale & retail | 2023 |
| JW Business Services Ltd | Financial services | 2021 |
| JWD Investments Ltd | Real estate | 2015 |
| JWR Carpentry & Building Ltd | Manufacturing | 2026 |
| Jwwlh Limited | Administrative & support | 2018 |
| JYJ Holdings UK Limited | Wholesale & retail | 2025 |
| JYY Holdings Limited | Financial services | 2024 |
| K & G Solutions Ltd | Construction | 2016 |
| K a H Electrical Limited | Construction | 2010 |
| K and OB Properties Limited | Administrative & support | 2026 |
| K D Kavanagh Ltd | Information & communication | 2022 |
| K Fuel (UK) Ltd | Wholesale & retail | 2012 |
| K Rama Construction Ltd | Construction | 2018 |
| K S Pharma Consultancy Limited | Health & social care | 2023 |
| K Sports Management Limited | Arts & recreation | 2016 |
| K Sports Soccer Limited | Arts & recreation | 2016 |
| K&C UK Investments Limited | Financial services | 2014 |
| K&M Films Limited | Information & communication | 2015 |
| K&R Brothers Limited | Real estate | 2017 |
| K&S Bajaria Ltd | Real estate | 2026 |
| K.E.R Properties Ltd | Real estate | 2019 |
| K19 Limited | Hospitality | 2002 |
| K4RIM Ltd | Real estate | 2018 |
| K622 Limited | Information & communication | 2014 |
| KA Capital Limited | Real estate | 2017 |
| Kabatia Ltd | Real estate | 2026 |
| Kabuki Child Care Centre Ltd | Education | 2013 |
| Kaca Contractors Ltd | Construction | 2025 |
| Kacey Limited | Administrative & support | 2014 |
| Kachcaro Ltd | Health & social care | 2020 |