| JKS Fleet Solutions Ltd | Transport & logistics | 2024 |
| JLM Property Services Ltd | Households | 2015 |
| JM Carehomes Limited | Administrative & support | 2006 |
| JM Facilities and Management Ltd | Extraterritorial | 2022 |
| JM Marketing Services Limited | Information & communication | 2019 |
| JMP Interiors Limited | Construction | 2009 |
| JMP Planning Limited | Professional & scientific | 2022 |
| JMS Commercial Lettings Ltd | Manufacturing | 2023 |
| JMS Financial Group Limited | Financial services | 2016 |
| JN Flooring Solutions Ltd | Construction | 2025 |
| JNC Retail Limited | Wholesale & retail | 2019 |
| Joaj IT Consulting Ltd | Information & communication | 2020 |
| Jobi Ltd | Health & social care | 2021 |
| JOE Jennings (Harlow) Limited | Arts & recreation | 2012 |
| JOE Jennings Crawley Limited | Arts & recreation | 2025 |
| Joekenna NIG Ltd | Health & social care | 2014 |
| John Brianne Rayvera Limited | Real estate | 2026 |
| John Galajsza Limited | Professional & scientific | 2014 |
| John James Clearance Ltd | Transport & logistics | 2018 |
| John James Ltd | Transport & logistics | 2018 |
| John Tinney & Co Limited | Agriculture & fishing | 1982 |
| Johnsons Roofing Specialist Limited | Construction | 2023 |
| Johtiva Health Services Ltd | Health & social care | 2025 |
| JOI Medics Limited | Health & social care | 2023 |
| Jojan Group of Companies Limited | Professional & scientific | 2023 |
| Jojostouch Ltd | Professional & scientific | 2025 |
| Jojovic Limited | Health & social care | 2021 |
| Jolliffeite Limited | Arts & recreation | 2021 |
| Jonescomm Services Ltd | Construction | 2018 |
| Jonessa Elite Properties Ltd | Real estate | 2026 |
| Jonseen Health Limited | Health & social care | 2023 |
| Jordan & Breen (Harlow) Limited | Administrative & support | 2000 |
| Jordi Construction Limited | Construction | 2021 |
| Jordin Construction Ltd | Manufacturing | 2025 |
| Jorellis Ltd | Real estate | 2025 |
| Josasuyi Ltd | Health & social care | 2022 |
| Josella Properties Ltd | Real estate | 2022 |
| Joseph Okolo Limited | Health & social care | 2025 |
| Joshua Holdings UK Ltd | Financial services | 2022 |
| Jovicky Properties Limited | Real estate | 2023 |
| Joy Danso Limited | Wholesale & retail | 2022 |
| Joy Flowers Limited | Wholesale & retail | 2026 |
| Joyacre Flat Management Company Limited | Households | 1990 |
| Joychristy Investment Limited | Health & social care | 2019 |
| Joymann Limited | Real estate | 2021 |
| Joyners Field 1957 Limited | Extraterritorial | 2014 |
| JP Heating and Plumbing Ltd | Construction | 2016 |
| JP Joll Limited | Hospitality | 2025 |
| JP Plant 360 Ltd | Construction | 2017 |
| JP6 Active Limited | Education | 2021 |
| JP6 Football Academy Limited | Education | 2020 |
| JPG Projects Limited | Professional & scientific | 2023 |
| Jpink Consulting Ltd | Real estate | 2019 |
| Jpinnah Ltd | Construction | 2025 |
| Jprh Limited | Arts & recreation | 2015 |
| JPS Group Services Limited | Administrative & support | 2016 |
| JPS Platforms Ltd | Administrative & support | 2014 |
| JRA & Co. Accounting and Consultancy Services Ltd | Professional & scientific | 2024 |
| JRW Motor Holdings Ltd | Financial services | 2019 |
| Jrwrightrenovations Limited | Construction | 2026 |
| Js&I Limited | Professional & scientific | 2024 |
| JSC Group Ltd | Construction | 2017 |
| JSJ Plant Ltd | Manufacturing | 2026 |
| Jssma Associates Limited | Education | 2020 |
| JTC Solutions Limited | Public administration | 2022 |
| JTD Property Group Ltd | Real estate | 2023 |
| Jtdw Holdings Limited | Wholesale & retail | 2016 |
| Jtech Irepair Limited | Manufacturing | 2021 |
| Jtfalcon Ltd | Construction | 2016 |
| JTL DRY Lining Ltd | Administrative & support | 2009 |
| Jubirsly Limited | Health & social care | 2023 |
| Jude Sullivan Limited | Health & social care | 2016 |
| Judges Building Services Ltd | Construction | 2020 |
| Judges Property Group Limited | Construction | 2026 |
| Julie's Care Ltd | Professional & scientific | 2023 |
| Julier & Jennings Homes Limited | Real estate | 2025 |
| Julier Homes Limited | Real estate | 2019 |
| Juloivi Limited | Other services | 2016 |
| Julozone Group Ltd | Health & social care | 2019 |
| Julpet Media Limited | Information & communication | 2025 |
| Jult Limited | Information & communication | 2026 |
| Jumoc Ltd | Wholesale & retail | 2019 |
| Junetoo International Limited | Administrative & support | 2023 |
| Juniper & Juniper Ltd | Real estate | 2022 |
| Junk 2 Clear Ltd | Water & waste | 2025 |
| Junk Force Ltd | Water & waste | 2023 |
| Junk Masters Limited | Professional & scientific | 2011 |
| Junk-Away Ltd | Water & waste | 2022 |
| Junora Medics Limited | Health & social care | 2026 |
| Just Filters Limited | Professional & scientific | 1997 |
| Just in Time Consulting Ltd | Wholesale & retail | 2015 |
| Just TAP IT Ltd | Hospitality | 2021 |
| Justacoon MC Ltd | Agriculture & fishing | 2021 |
| Justbest Care Limited | Health & social care | 2019 |
| JW Clothing Ltd | Wholesale & retail | 2025 |
| JW Contour Holdings Limited | Financial services | 2015 |
| JW Drains Limited | Construction | 2023 |
| JW FFF Coaching LLP | | 2026 |
| JW International Trading Limited | Wholesale & retail | 2025 |
| JWC Property Holdings Ltd | Real estate | 2024 |