| Joseph Payne (Colne Valley) Limited | Professional & scientific | 1952 |
| Joshr Limited | Real estate | 2024 |
| Josmeken (PVT) Ltd | Construction | 2014 |
| Joteco Limited | Health & social care | 2019 |
| Journeyman Portfolio Ltd | Real estate | 2018 |
| Jovid Services Limited | Other services | 2019 |
| Jowle Cars Ltd | Transport & logistics | 2022 |
| Joyalicious Limited | Wholesale & retail | 2025 |
| JP Carpentry & Joinery Ltd | Construction | 2017 |
| Jpcarzone Ltd | Wholesale & retail | 2023 |
| JPG Construction Services Ltd | Construction | 2015 |
| JPM Fleetcare Ltd | Manufacturing | 2018 |
| JR Auto Group Limited | Wholesale & retail | 2026 |
| Jr&S Consultancy Services Ltd | Professional & scientific | 2023 |
| Jreg Properties Limited | Real estate | 2024 |
| Jrek Ltd | Real estate | 2022 |
| JRM Associates Properties Ltd | Real estate | 2022 |
| JRM Medical Services Ltd | Health & social care | 2018 |
| JRS Direct Developments Limited | Real estate | 2026 |
| JS Aurex Ltd | Real estate | 2026 |
| Jsdk Educational Services Limited | Education | 2014 |
| JSK UK Properties Limited | Households | 2020 |
| JT Accounts Limited | Professional & scientific | 2016 |
| JT Fashion Consultancy Ltd | Wholesale & retail | 2025 |
| JTG Asset Management Limited | Construction | 2018 |
| JTT Utilities & Civils Ltd | Construction | 2022 |
| Jubabital Limited | Other services | 2021 |
| Jubilee Church London Ltd | Education | 2014 |
| Judywood Ltd | Wholesale & retail | 2020 |
| Jufo Ltd | Wholesale & retail | 2022 |
| Jugo Ventures Ltd | Wholesale & retail | 2025 |
| Jukel Property Limited | Real estate | 2024 |
| Julia-Louise-Ruthlyn Roberts | Extraterritorial | 2023 |
| Julie 99 Limited | Other services | 2019 |
| Julie MAY Ltd | Administrative & support | 2014 |
| Julliz Law Ltd | Professional & scientific | 2014 |
| Julliz Solicitors LLP | | 2010 |
| July Nails & Spa Limited | Other services | 2021 |
| Jumbo Cash & Carry Limited | Wholesale & retail | 2014 |
| Junction Services Ltd | Real estate | 1999 |
| Junglees Enfield Ltd | Hospitality | 2025 |
| Juniper Care Limited | Health & social care | 2011 |
| Juno Ventures Limited | Professional & scientific | 2020 |
| Junora Atelier Limited | Wholesale & retail | 2026 |
| Jura Foods Ltd | Wholesale & retail | 2004 |
| Jura Group Ltd | Wholesale & retail | 2019 |
| Jura Logistics Limited | Transport & logistics | 2021 |
| Jura Lounge Ltd | Hospitality | 2022 |
| Jura Trading Limited | Wholesale & retail | 2000 |
| Jura Wholesale Ltd | Wholesale & retail | 2019 |
| Jurique Limited | Information & communication | 2015 |
| JUS U Limited | Other services | 2015 |
| Just a Must Limited | Arts & recreation | 2011 |
| Just Care Properties Ltd | Construction | 2021 |
| Just Hire Ltd | Administrative & support | 2025 |
| Just in Renovation Limited | Construction | 2024 |
| Just Rank Ltd | Professional & scientific | 2026 |
| Justantique Limited | Wholesale & retail | 2025 |
| Justcommunicate Training Ltd | Information & communication | 2026 |
| Justice for Tenants Ltd | Information & communication | 2016 |
| Justt Ltd | Wholesale & retail | 2026 |
| JV Maintenance Ltd | Construction | 2024 |
| JV Nails Spa Claygate Limited | Other services | 2019 |
| JV Property Solutions Limited | Real estate | 2016 |
| JVH Property Limited | Real estate | 2024 |
| JW Legal Care Services Ltd | Professional & scientific | 2018 |
| JWB Services Limited | Construction | 2002 |
| JWJ Travels Ltd | Administrative & support | 2025 |
| JWM Solutions Ltd | Administrative & support | 2016 |
| JWS Energy Assessors Limited | Professional & scientific | 2025 |
| Jwsupplied Ltd | Wholesale & retail | 2025 |
| JXB Properties Ltd | Real estate | 2024 |
| Jyotika Limited | Financial services | 2022 |
| JZS Construction Ltd | Construction | 2020 |
| K & L Interior Ltd | Manufacturing | 2018 |
| K & W Ceiling Limited | Construction | 2017 |
| K 1 Furnishings Ltd | Wholesale & retail | 2006 |
| K American Nails Ltd | Other services | 2013 |
| K and a Accountants Limited | Professional & scientific | 2010 |
| K Brothers Logistics Ltd | Transport & logistics | 2021 |
| K Class Construction Ltd | Construction | 2025 |
| K F Electrical Services Limited | Construction | 2008 |
| K G S Property Solutions Ltd | Construction | 2017 |
| K Hajikypri Limited | Extraterritorial | 2006 |
| K Jessica Mays Limited | Other services | 2019 |
| K Kitch Ltd | Hospitality | 2024 |
| K Lawlor Properties Ltd | Real estate | 2022 |
| K Mihov Limited | Construction | 2018 |
| K Physio Ltd | Health & social care | 2008 |
| K PYN Ltd | Financial services | 2024 |
| K Roofing Ltd | Construction | 2021 |
| K V S Mohan London Limited | Construction | 2009 |
| K&K Kent Nails Limited | Other services | 2019 |
| K&K Levi Ltd | Health & social care | 2025 |
| K&L Bathroom Tiles & Walls & Floors Ltd | Construction | 2025 |
| K&S Builders Ltd | Construction | 2026 |
| K&Y Mechanical Limited | Manufacturing | 2018 |
| K-Mojo Limited | Wholesale & retail | 2024 |
| K-N Nails 1 Limited | Other services | 2025 |
| K-Side Design Limited | Professional & scientific | 2008 |