| J3 Solutions Limited | Professional & scientific | 1998 |
| J316LONDON Ltd | Wholesale & retail | 2024 |
| JA & Co Accounting Limited | Professional & scientific | 2017 |
| JA Associates Services Ltd | Professional & scientific | 2025 |
| JA Homes Limited | Real estate | 2015 |
| JA Jewels Ltd | Wholesale & retail | 2018 |
| JA Lashes and Co Ltd | Wholesale & retail | 2026 |
| JA Prime Ltd | Wholesale & retail | 2024 |
| JA Safety Certificates Ltd | Other services | 2020 |
| Ja&P Limited | Wholesale & retail | 2020 |
| JAA London Ltd | Real estate | 2022 |
| Jaan Housing Ltd | Real estate | 2021 |
| JAB Creative Ltd | Information & communication | 2025 |
| Jabrador Ltd | Other services | 2024 |
| JAC International Limited | Real estate | 2024 |
| JAC Traders Limited | Wholesale & retail | 2014 |
| Jacaranda Florists Limited | Wholesale & retail | 2011 |
| Jack & AMI Ltd | Wholesale & retail | 2020 |
| Jack and Jills Property Ltd | Real estate | 2024 |
| Jack Cornwell 1 Ltd | Construction | 2021 |
| Jack Day Properties Limited | Real estate | 2016 |
| Jack Interiors Limited | Construction | 1997 |
| Jackson Units Limited | Hospitality | 2025 |
| Jacksons Children's Home Ltd | Health & social care | 2024 |
| Jacksons Holdings LLP | | 2016 |
| Jackss Consulting Ltd. | Information & communication | 2015 |
| Jackss Housing Services Ltd | Real estate | 2022 |
| Jacmki Limited | Financial services | 2022 |
| Jaco Bathrooms Limited | Construction | 2015 |
| Jacob & Riley Heating Ltd | Construction | 2019 |
| Jacob's Academy Trading Ltd | Construction | 2025 |
| Jacobs Sassoon Limited | Financial services | 2002 |
| Jacques Property Limited | Real estate | 2019 |
| JAD Consultancy Ltd | Health & social care | 2024 |
| JAD IT Consultancy Limited | Information & communication | 2017 |
| JAD Tech Limited | Other services | 2026 |
| Jade International Limited | Other services | 2020 |
| Jadebright Limited | Real estate | 2020 |
| Jademark Limited | Wholesale & retail | 2023 |
| Jadi Motors Ltd | Wholesale & retail | 2019 |
| Jadicar Ltd | Wholesale & retail | 2025 |
| Jadoon Ltd | Hospitality | 2023 |
| Jadu Drinks Ltd | Wholesale & retail | 2024 |
| Jaff's Resto Ltd | Hospitality | 2026 |
| Jaffar Traders Limited | Information & communication | 2026 |
| Jaffer Bhai's Delhi Darbar Restaurant (Bombay) Limited | Professional & scientific | 2004 |
| JAG Gears UK Ltd | Wholesale & retail | 2024 |
| JAG Shaving UK Ltd | Wholesale & retail | 2024 |
| Jagal Limited | Construction | 2024 |
| Jagdeep Singhh Ltd | Construction | 2025 |
| Jagpharma UK Limited | Wholesale & retail | 2009 |
| Jagrit Singh Ltd | Construction | 2025 |
| Jagstar Limited | Extraterritorial | 2009 |
| JAH Care Ltd | Health & social care | 2020 |
| Jahangir Holdings Ltd | Administrative & support | 2024 |
| Jahangir Hussain Limited | Professional & scientific | 2002 |
| Jahmik Consulting Ltd | Information & communication | 2014 |
| Jahromi Properties Ltd | Real estate | 2024 |
| JAI Capital Holdings Ltd | Financial services | 2025 |
| JAI Solutions Ltd | Information & communication | 2025 |
| Jaibrisa Investments UK Ltd | Real estate | 2018 |
| Jaidad Developers Ltd | Professional & scientific | 2025 |
| Jaidh Consultancy Limited | Professional & scientific | 2022 |
| Jaidh Properties Limited | Real estate | 2024 |
| Jaison Guest House Ltd | Hospitality | 2020 |
| Jakas Traders Ltd | Construction | 2025 |
| Jakdshan Ltd | Wholesale & retail | 2025 |
| Jake Henry Plasterers Ltd | Construction | 2021 |
| Jaks Essentials Ltd | Wholesale & retail | 2025 |
| Jaks Mens Grooming Ltd | Other services | 2024 |
| Jaku & Co Limited | Construction | 2018 |
| Jakukiki Properties Ltd | Real estate | 2021 |
| Jakup Construction Limited | Construction | 2022 |
| Jalal Group Ltd | Wholesale & retail | 2024 |
| Jaldise Ltd | Wholesale & retail | 2024 |
| Jalf Lettings & Management Ltd | Real estate | 2025 |
| JAM Automations Ltd | Information & communication | 2023 |
| JAM Care Solutions Ltd | Health & social care | 2023 |
| Jamaima Fashions Ltd | Wholesale & retail | 2022 |
| Jamal Consulting Ltd | Professional & scientific | 2014 |
| Jaman Bhai Enterprises Ltd | Wholesale & retail | 2019 |
| James & Sons Distilleries UK Ltd | Mining & quarrying | 2020 |
| James Consult Ltd | Professional & scientific | 2020 |
| James Hameed Productions Ltd | Arts & recreation | 2025 |
| James Hilton House Management Limited | Households | 1982 |
| James Jordan Construction Ltd | Construction | 2025 |
| James Linton Limited | Information & communication | 2023 |
| Jamia Noor UL Quran and Community Centre | Education | 2018 |
| Jamia Rauzatussalihat | Health & social care | 2023 |
| Jamiat-E-Ulama-E-Islam UK Ltd | Other services | 2025 |
| Jamie Kitchen Electrical Ltd | Construction | 2019 |
| Jamie Stephen Limited | Professional & scientific | 2005 |
| Jamik & Co Limited | Wholesale & retail | 2015 |
| Jammms FI LLP | | 2017 |
| Jammu Construction London Ltd | Construction | 2026 |
| JAN Piotr Property Maintenance Ltd | Construction | 2015 |
| Janacleaning Limited | Administrative & support | 2019 |
| Janadhan Ltd | Wholesale & retail | 2025 |
| Janahi Engineering Ltd | Construction | 2016 |
| JANAND2022 Limited | Professional & scientific | 2022 |