| JCE Legal Services Limited | Professional & scientific | 2026 |
| JCM Community Care Limited | Health & social care | 2017 |
| Jcs-Hw Ltd | Wholesale & retail | 2025 |
| JCW Engineering Consultants Limited | Mining & quarrying | 2014 |
| JD Media Limited | Information & communication | 2012 |
| JD Professional Services Ltd | Professional & scientific | 2025 |
| JD Property Estate Ltd | Real estate | 2026 |
| JDC Illustration Limited | Information & communication | 2014 |
| JDS Films Limited | Information & communication | 2013 |
| Jebac PIS Ltd | Professional & scientific | 2020 |
| JEE House Management Ltd | Households | 2024 |
| Jeet Ventures Ltd | Wholesale & retail | 2025 |
| Jeeto London Ltd | Professional & scientific | 2024 |
| Jeffark Engineering and Metal Pressings Limited | Manufacturing | 1988 |
| Jeffark Ltd | Financial services | 2023 |
| Jemma Crafts Limited | Other services | 2017 |
| Jenna Bent Send Ltd | Education | 2025 |
| Jenner Landscapes Ltd | Administrative & support | 2024 |
| Jenny's Fashions Limited | Real estate | 2003 |
| Jenny's Fashions NO 1 Ltd | Real estate | 2020 |
| Jensten Insurance Brokers (Thames Valley) Ltd | Financial services | 1974 |
| Jeremie Delivery Service Ltd | Transport & logistics | 2020 |
| Jersey Guys Ltd | Arts & recreation | 2013 |
| JES Jones Ltd | Health & social care | 2015 |
| Jesus Apostolic International Ministry Ltd | Information & communication | 2024 |
| JET INT Trading Ltd | Wholesale & retail | 2023 |
| JGN Ltd | Information & communication | 2023 |
| JGS Partners & Investment Ltd | Wholesale & retail | 2020 |
| Jhaaap Ltd | Professional & scientific | 2024 |
| JHB Commerce Limited | Wholesale & retail | 2024 |
| JHC Electrical Services Ltd | Construction | 2011 |
| JHD Productions Limited | Other services | 2017 |
| JHI Property Ltd | Real estate | 2025 |
| Jhon Limited | Construction | 2017 |
| Jhonny Handyman Ltd | Manufacturing | 2019 |
| Jhutty Properties Limited | Real estate | 2022 |
| Jigsaw Internet Ltd | Information & communication | 2012 |
| Jigsaw Power Ltd | Professional & scientific | 2024 |
| Jilani Trading Services Limited | Wholesale & retail | 2022 |
| Jill Littlejohn Limited | Professional & scientific | 2020 |
| Jill Martin Event Management Limited | Professional & scientific | 2012 |
| JIM 1 Limited | Extraterritorial | 1933 |
| JIM 3 Limited | Extraterritorial | 1961 |
| JIM 4 Limited | Extraterritorial | 1916 |
| JIM 5 Limited | Extraterritorial | 1967 |
| Jimmy Vibes Ltd | Wholesale & retail | 2026 |
| Jimmys Pizza High Wycombe Ltd | Hospitality | 2024 |
| JIN Consulting Limited | Professional & scientific | 2019 |
| Jiten Parekh Limited | Real estate | 2016 |
| JJ Cleaning London Ltd | Administrative & support | 2020 |
| JJ HMO Estate Ltd | Real estate | 2023 |
| JJ Rental Properties Ltd | Real estate | 2025 |
| Jj-Welburn Holdings Limited | Professional & scientific | 2016 |
| JJA Town Planning Limited | Professional & scientific | 2020 |
| Jjad Limited | Professional & scientific | 2005 |
| JJS Services Ltd | Construction | 2026 |
| JK Electrical Solutions Ltd | Construction | 2019 |
| JK Hygiene Limited | Health & social care | 2026 |
| JK W4 Contractors Ltd | Construction | 2018 |
| Jk&Pk Construction Ltd | Construction | 2021 |
| JK66 Car Sales Ltd | Wholesale & retail | 2025 |
| JKB Hudds Ltd | Agriculture & fishing | 2024 |
| Jkp-Estates Ltd | Real estate | 2017 |
| Jkrk Properties Limited | Real estate | 2018 |
| JL Services Limited | Administrative & support | 2015 |
| Jlcg Ltd | Professional & scientific | 2024 |
| JLH Accountancy Limited | Other services | 2019 |
| JLR Maintenance Limited | Construction | 2006 |
| JM Global Infotech Ltd | Information & communication | 2016 |
| JM Rose Building Ltd | Construction | 2026 |
| JM Wines Ltd | Wholesale & retail | 2019 |
| JMC Heating and Plumbing Ltd | Construction | 2020 |
| JMC Security Limited | Administrative & support | 2023 |
| JMP Coaching & PT Ltd | Health & social care | 2025 |
| JMR Electrical Contractors Limited | Construction | 2002 |
| Jmsecure-It Ltd | Information & communication | 2025 |
| JMZ Properties Ltd | Real estate | 2021 |
| JN Accounting & Taxation Services Limited | Professional & scientific | 2020 |
| JN Consulting Ltd | Professional & scientific | 2022 |
| JN Global Care Ltd | Administrative & support | 2022 |
| JN Physiotherapy Ltd | Health & social care | 2023 |
| Jnas Moulding Limited | Information & communication | 2026 |
| Jntc Limited | Health & social care | 2011 |
| JO Wander Management Limited | Administrative & support | 2008 |
| JO Yeomans Consultancy Ltd | Professional & scientific | 2022 |
| Joanna Roberts Bridal Limited | Wholesale & retail | 2024 |
| Jobanputra Investments Ltd | Other services | 2023 |
| Joefergraphy Limited | Information & communication | 2025 |
| Jogia Ventures Ltd | Financial services | 2025 |
| Johanna Potkin Consultancy Ltd | Administrative & support | 2022 |
| John Arnison Music and Media Limited | Professional & scientific | 2013 |
| John Enterprise Ltd | Wholesale & retail | 2025 |
| John Ford Lighting and Vision Limited | Information & communication | 2005 |
| John Hampden Grammar School | Education | 2011 |
| John Hopkins (Building) Limited | Extraterritorial | 1944 |
| John Hopkins Estate Limited | Real estate | 1941 |
| John LEE Construction Limited | Construction | 2004 |
| John Murphy Financial Management Limited | Professional & scientific | 2019 |
| John Whitby Limited | Information & communication | 2012 |
| Johnson Health Tech Digital UK Limited | Information & communication | 2021 |