| J.W. Properties (London) Limited | Construction | 2006 |
| J2 Plumbing Ltd | Construction | 2025 |
| J2 Scaffolding Ltd | Construction | 2018 |
| J2SKI Limited | Arts & recreation | 2006 |
| Jabaclisem Limited | Other services | 2016 |
| Jabbs.Com Limited | Information & communication | 2004 |
| Jacaranda Pictures Limited | Information & communication | 2023 |
| Jacket Games Ltd | Information & communication | 2025 |
| Jackpot Insurance Consultancy Limited | Professional & scientific | 2017 |
| Jackpot Property Consultancy Ltd | Real estate | 2017 |
| Jackson Moss Transport Group Ltd | Transport & logistics | 2021 |
| Jackson Torq Systems Ltd | Wholesale & retail | 2016 |
| JAD Configuration Limited | Information & communication | 2022 |
| Jadexe Ltd | Manufacturing | 2019 |
| Jagroofing Ltd | Construction | 2024 |
| Jalali Spice Ltd | Hospitality | 2019 |
| James and Joy Limited | Professional & scientific | 2021 |
| James Dove Properties Ltd | Real estate | 2024 |
| James Frank Developments Limited | Real estate | 2022 |
| James Hackney Scenic Ltd | Information & communication | 2022 |
| James Harris Corporate Travel Limited | Transport & logistics | 2021 |
| James HOW Music Strings Limited | Extraterritorial | 2012 |
| James Mitchell Events Ltd | Professional & scientific | 2011 |
| James R Brown & Company Limited | Construction | 2015 |
| Jameshatha Limited | Construction | 2018 |
| Jamie Burrows Coaching Limited | Administrative & support | 2019 |
| Jamie Burrows Events Limited | Administrative & support | 2026 |
| Jamsheer Ltd | Professional & scientific | 2017 |
| Janika Limited | Wholesale & retail | 2023 |
| Januarius Limited | Real estate | 2012 |
| JAP Retro Ltd | Wholesale & retail | 2015 |
| Jardox Limited | Manufacturing | 1922 |
| Jarkholmen Consulting Ltd | Wholesale & retail | 2020 |
| JAS & Co Group Limited | Real estate | 2026 |
| JAS Papa Johns Limited | Hospitality | 2012 |
| Jasapa Ltd | Real estate | 2024 |
| Jason's Contracts Limited | Construction | 2003 |
| Jasonsoft Ltd | Administrative & support | 2016 |
| JAX Designer Classics Limited | Wholesale & retail | 1998 |
| JAY Bird Limited | Professional & scientific | 2023 |
| JAY Kelly Golf Coaching Ltd | Arts & recreation | 2025 |
| JAY Kelly Golf Limited | Arts & recreation | 2020 |
| Jayne Reese Limited | Administrative & support | 2002 |
| Jazady Investments Ltd | Financial services | 2018 |
| JB and D Limited | Real estate | 2012 |
| JB Landscape & Garden Management Ltd | Administrative & support | 2021 |
| Jbwroofing Services Ltd | Construction | 2019 |
| JC Contemporary Ltd. | Wholesale & retail | 2016 |
| Jcab Limited | Administrative & support | 2025 |
| JCF Medico Limited | Health & social care | 2015 |
| JD Construction Ltd | Construction | 2025 |
| Jdbventures Ltd | Information & communication | 2026 |
| JDP E-Commerce Ltd | Wholesale & retail | 2026 |
| Jeensbannet Investments Limited | Real estate | 1964 |
| Jefcut Capital Partners Ltd | Financial services | 2024 |
| Jeffs Carry on Camping Farm Enterprises Ltd | Hospitality | 2019 |
| Jellygram Limited | Manufacturing | 2015 |
| Jellymould Limited Liability Partnership | | 2016 |
| Jennifer Ebert Consulting Ltd | Professional & scientific | 2018 |
| Jeremy's Home Store Limited | Wholesale & retail | 2004 |
| Jessups (Lime Productions) Limited | Mining & quarrying | 1935 |
| JET Offham Ltd | Wholesale & retail | 2024 |
| Jetflight Limited | Transport & logistics | 2006 |
| Jevaughny Jean Consultancy Ltd | Professional & scientific | 2024 |
| JFC Building Services Limited | Construction | 2008 |
| JFK Bros Limited | Administrative & support | 2023 |
| JG Global Legal Consultants LLP | | 2011 |
| JG Specialist Property Services Limited | Real estate | 2025 |
| Jgmpr Ltd | Professional & scientific | 2017 |
| JH Advisory Group Ltd | Administrative & support | 2025 |
| JH Alpha Limited | Extraterritorial | 2025 |
| Jhkc Ltd | Professional & scientific | 2021 |
| JI Creative Limited | Professional & scientific | 2022 |
| JI Design Ltd | Professional & scientific | 2024 |
| Jibidy Limited | Arts & recreation | 2012 |
| JIF Enterprises Limited | Extraterritorial | 2015 |
| JIG & JAY Limited | Real estate | 2019 |
| JIM Bellingham Associates Limited | Professional & scientific | 2006 |
| JJ Party & Events Limited | Administrative & support | 2024 |
| Jj's Kentish Garden Creations Ltd | Agriculture & fishing | 2025 |
| JJC Maintenance Ltd | Construction | 2023 |
| JK Contractors South East Ltd | Construction | 2019 |
| JK Estate Maintenance Ltd | Professional & scientific | 2022 |
| JK Marketing Ltd | Extraterritorial | 2025 |
| JL Miranda Ltd | Health & social care | 2013 |
| JLJ Estates Limited | Construction | 2017 |
| Jmbc Limited | Professional & scientific | 2024 |
| JML Home Services Limited | Other services | 2026 |
| JMS Growth Limited | Professional & scientific | 2016 |
| JNP Roofing Ltd | Construction | 2024 |
| JO Jemmison Garden and Landscape Design Ltd | Administrative & support | 2018 |
| Joan Perkins Limited | Professional & scientific | 2019 |
| Joanna Lands Limited | Administrative & support | 2005 |
| Jobrooms Systems Ltd | Administrative & support | 2023 |
| JOBS4COUPLES Limited | Administrative & support | 2023 |
| Joco Enterprises Ltd | Real estate | 2017 |
| John Anthony Grogan Ltd | Extraterritorial | 2024 |
| John Hinge (Spitalfields) Limited | Wholesale & retail | 1960 |
| John Mower (Kent) Limited | Transport & logistics | 2013 |
| John Purdie Consulting Limited | Professional & scientific | 2014 |