| Johns Hair Stylists Limited | Other services | 2014 |
| Joke & Craft Ltd | Wholesale & retail | 2022 |
| JON & on Ltd | Information & communication | 2021 |
| Jones & Sons Properties Limited | Real estate | 2022 |
| Jones Elite Ltd | Health & social care | 2022 |
| Jones Road Productions Ltd | Information & communication | 2023 |
| Joniferon Services Ltd | Administrative & support | 2012 |
| Jonjo Leisure Limited | Hospitality | 2018 |
| Jordyinit Ltd | Information & communication | 2020 |
| Jorn Ltd | Construction | 2025 |
| Joseph David Group Ltd | Health & social care | 2025 |
| Joshis Computer Limited | Information & communication | 2010 |
| Journey Mentor Holdings Ltd | Financial services | 2023 |
| Joy 7 Ltd | Transport & logistics | 2022 |
| Joy Canteen Limited | Hospitality | 2019 |
| Joy Properties Ltd | Real estate | 2025 |
| Joy Vend Ltd | Wholesale & retail | 2026 |
| Joya Aesthetic and Beauty Ltd | Other services | 2024 |
| Joycie Services Limited | Health & social care | 2020 |
| Joymex Consultants Limited | Information & communication | 2005 |
| JP Hyper Investments Ltd | Financial services | 2021 |
| JPG Floors Limited | Construction | 2021 |
| Jpgold Analytics Ltd | Professional & scientific | 2018 |
| JPS Real Estate Development Ltd | Construction | 2005 |
| Jrbn Consulting Limited | Financial services | 2012 |
| JRF Project Management Services LLP | | 2014 |
| JRL Plumbing and Heating Engineers Ltd | Construction | 2023 |
| JRS Financial Ltd | Professional & scientific | 2025 |
| Jrwt Limited | Professional & scientific | 2008 |
| JS Tech Pharma Ltd | Wholesale & retail | 2016 |
| JSC Productions Limited | Manufacturing | 2025 |
| JSC Signalling Ltd | Construction | 2022 |
| JSJ Automotive Ltd | Wholesale & retail | 2022 |
| JSM Construction London Ltd | Construction | 2021 |
| JSM Investments Havering Limited | Real estate | 2025 |
| JSS Digital Ltd | Wholesale & retail | 2018 |
| JSS Entertainment Ltd | Hospitality | 2023 |
| JTM Properties Limited | Real estate | 2021 |
| Jubany Holdings Ltd | Real estate | 2024 |
| Jubilee Plastics Limited | Other services | 2012 |
| Juicy Chicken Rotisserie Co Ltd | Hospitality | 2019 |
| Juju's! the Style Closet Ltd | Wholesale & retail | 2023 |
| Jules Flooring Limited | Construction | 2023 |
| Julio Ltd | Other services | 2024 |
| Jumart Healthcare Limited | Health & social care | 2023 |
| Jungle Safety Ltd | Professional & scientific | 2019 |
| Junior Activity Club Ltd | Arts & recreation | 2022 |
| Just Talent Entertainment Ltd | Arts & recreation | 2013 |
| Just Teeth Limited | Health & social care | 2016 |
| JUSTCLEAN4U Limited | Other services | 2026 |
| JUSTUNIQ4U UK Limited | Hospitality | 2022 |
| JVM Civils Ltd | Construction | 2024 |
| JW Signals Ltd | Professional & scientific | 2023 |
| JWB Transport Services Limited | Transport & logistics | 2001 |
| K and S Cabling Limited | Construction | 1997 |
| K Bartlett Investments Limited | Real estate | 2020 |
| K Bater Consultancy Limited | Professional & scientific | 2013 |
| K Brown Professional Services Limited | Professional & scientific | 2014 |
| K D Windows & Doors Limited | Construction | 2019 |
| K K Property Solutions Limited | Households | 2026 |
| K Pullin Financial Solutions Limited | Professional & scientific | 2018 |
| K&V Group Ltd | Real estate | 2025 |
| K&Z Investments Ltd | Real estate | 2025 |
| K1 FIX & Drive Ltd | Wholesale & retail | 2025 |
| Kaan Amjad Limited | Manufacturing | 2017 |
| Kaarsp Limited | Real estate | 2016 |
| Kabbas Gifts Ltd | Wholesale & retail | 2021 |
| Kacey Homes Limited | Real estate | 2020 |
| Kaindal Property Ltd | Real estate | 2023 |
| Kains Consultancy Ltd | Real estate | 2022 |
| Kalo Living Ltd | Health & social care | 2025 |
| KAM Property Investments Limited | Real estate | 2015 |
| Kamal & Sons Property Limited | Construction | 2025 |
| Kamal Property Investments Limited | Real estate | 2018 |
| Kamara Property Services Ltd | Real estate | 2024 |
| Kambani Arts | Arts & recreation | 2005 |
| Kameroo Ltd | Wholesale & retail | 2017 |
| Kamis Estates Ltd | Real estate | 2017 |
| Kampek Ltd | Construction | 2024 |
| Kanha Consulting Limited | Information & communication | 2015 |
| Kaninio Ltd | Information & communication | 2019 |
| Kankam Group Properties Ltd | Real estate | 2023 |
| Kansley Ltd | Real estate | 2024 |
| Kanthan & Co Ltd | Professional & scientific | 2002 |
| Kanthan Medics Ltd | Professional & scientific | 2024 |
| Kanthan Properties Ltd | Real estate | 2021 |
| Kantor IT Consulting Group Limited | Professional & scientific | 2016 |
| KAO Thai Limited | Hospitality | 2025 |
| Kaot Home Care Ltd | Health & social care | 2022 |
| Kaot Resources Limited | Wholesale & retail | 2008 |
| Kapila Properties Ltd | Real estate | 2022 |
| Kapila Ventures Limited | Real estate | 2025 |
| Kaprice Management Solutions Ltd | Professional & scientific | 2017 |
| KARE4U Ltd | Administrative & support | 2019 |
| Karlsen Consulting Ltd | Professional & scientific | 2020 |
| Karolina 8 Limited | Health & social care | 2011 |
| Kartar Homes Ltd | Construction | 2021 |
| Kartar Property Ltd | Real estate | 2025 |
| KAS Enhanced Trading Limited | Real estate | 2015 |
| Kasd Renova Ltd | Construction | 2019 |