| John Lift Hire Ltd | Wholesale & retail | 2025 |
| John Lyon Court Limited | Real estate | 2025 |
| John Milverton Limited | Wholesale & retail | 1947 |
| John Nicholls & Sons Limited | | 1935 |
| John O'Connor Plastering Limited | Construction | 2007 |
| John Pargeter & Sons Limited | Wholesale & retail | 1964 |
| John Paul Properties Ltd | Real estate | 2019 |
| John Philip Ltd | Construction | 2020 |
| John Phillips Metals Limited | Manufacturing | 1984 |
| John Price (JP) Limited | Administrative & support | 2009 |
| John Price Printers Limited | Administrative & support | 1993 |
| John Price TM Ltd | Construction | 2025 |
| John Property Ltd | Real estate | 2022 |
| John Rublea Construction Ltd | Manufacturing | 2018 |
| John Russell Holdings Limited | Financial services | 2007 |
| John Russell Insurance Services Limited | Financial services | 1998 |
| John Saul (& Sons) Construction Ltd | Construction | 2004 |
| John Simpson Kitchens Ltd | Construction | 2026 |
| John Smith (Blackheath) Limited | Manufacturing | 1966 |
| John Smith Facilities Limited | Real estate | 1972 |
| John Stait & Company Limited | Extraterritorial | 1973 |
| John Street (Derby) Limited | Administrative & support | 2019 |
| John Wesley Estate Limited | Real estate | 2019 |
| John Wilde & Co.(Metals)Limited | Manufacturing | 1960 |
| John Yates Design Limited | Professional & scientific | 2015 |
| John Yorke Holdings Limited | Financial services | 2023 |
| John's Balti Ltd | Hospitality | 2025 |
| John's Blinds Direct Ltd | Manufacturing | 2025 |
| John's Property Services Ltd | Construction | 2020 |
| Johnnies Enterprises UK Limited | Wholesale & retail | 2024 |
| Johnny Topco Limited | Financial services | 2018 |
| Johns Chippy Ltd | Hospitality | 2026 |
| Johnson Bespoke Limited | Manufacturing | 2016 |
| Johnson Bros. Limited | Wholesale & retail | 2009 |
| Johnson Energy Solutions Ltd | Construction | 2011 |
| Johnson Fellows LLP | | 2007 |
| Johnson Fleming Future Life Planning Limited | Financial services | 2014 |
| Johnson Fleming Group Limited | Professional & scientific | 2007 |
| Johnson Fleming Limited | Financial services | 2002 |
| Johnson Fleming Services Limited | Financial services | 2013 |
| Johnson Jones Ltd | Construction | 2014 |
| Johnson Supplies UK Ltd | Manufacturing | 2018 |
| Johnson's Grab Hire Limited | Transport & logistics | 2017 |
| Johnson's Property Management (UK) Ltd | Administrative & support | 2007 |
| Johnsons Coldrooms Limited | Construction | 2022 |
| Johnsons Developments Ltd | Construction | 2013 |
| Johnsons Timber Services Ltd | Wholesale & retail | 2009 |
| Johnsons Timber Supplies Limited | Wholesale & retail | 1978 |
| Johntempleton.Org Limited | Information & communication | 2009 |
| Johny Building Construction Ltd | Construction | 2026 |
| JOI 11 Tech Ltd | Other services | 2026 |
| Joie DE Vivre Ventures Community Interest Company | Education | 2018 |
| Joinery & Refurbishment Projects Limited | Construction | 2019 |
| Joinery Services Ltd | Construction | 2008 |
| Joinpoint Contractors Limited | Other services | 1993 |
| Joinpoint Limited | Construction | 1988 |
| Joint Commercial Building Services Limited | Manufacturing | 2013 |
| Joint Courier Express Ltd | Transport & logistics | 2024 |
| Joint Pain Clinics Ltd | Health & social care | 2024 |
| Joint Prodigy Limited | Financial services | 2021 |
| Joint Surgery Private Limited | Health & social care | 2015 |
| Joint Vision Limited | Health & social care | 2018 |
| Joiv Healthcare Ltd | Health & social care | 2023 |
| Jojjii Limited | Transport & logistics | 2019 |
| Jojo & Maylis Ltd | Transport & logistics | 2025 |
| Jojo Stat Ltd | Hospitality | 2023 |
| Jojo's Bakery Limited | Manufacturing | 2025 |
| Jojoflow Limited | Transport & logistics | 2025 |
| Joju Healthcare Ltd | Health & social care | 2015 |
| Jokalian Online Ltd | Wholesale & retail | 2025 |
| Jola SAM Limited | Public administration | 2026 |
| Jole Consultancy Limited | Information & communication | 2026 |
| Jole Estates Ltd | Real estate | 2019 |
| Joli Beauty Aesthetics Ltd | Other services | 2021 |
| Jolla Construction Ltd | Construction | 2022 |
| Jolla Imports Ltd | Wholesale & retail | 2026 |
| Jollof and More UK Ltd | Hospitality | 2025 |
| Jollof Station Ltd | Hospitality | 2025 |
| Jolly BEE Ltd | Information & communication | 2021 |
| Jolly Tots Ltd | Wholesale & retail | 2005 |
| Jolly Totts 24/7 Ltd | Health & social care | 2015 |
| Jollyamand Ltd | Arts & recreation | 2025 |
| Jolob Cafe Shop Ltd | Hospitality | 2023 |
| Jolotrading Company Ltd | Hospitality | 2019 |
| Jomash Ventures Ltd | Education | 2023 |
| Jomatt Property Investments (UK) Limited | Real estate | 2025 |
| Jomore Limited | Real estate | 2021 |
| Jomyuk Limited | Real estate | 2020 |
| JON Addis Consulting Limited | Professional & scientific | 2023 |
| JON Clugston Properties Ltd | Real estate | 2019 |
| JON Doors Ltd | Wholesale & retail | 2011 |
| JON Jones Art Limited | Construction | 2021 |
| JON Kong Productions Limited | Information & communication | 2020 |
| JON Logiistic Ltd | Transport & logistics | 2021 |
| JON Paul (Fashions) Limited | Wholesale & retail | 1978 |
| Jonado Pharmaceutical Services Limited | Health & social care | 2025 |
| Jonah Banks & Sons Limited | Manufacturing | 1973 |
| Jonah's Project CIC | Education | 2017 |
| Jonapoo Ltd | Wholesale & retail | 2025 |
| Jonathan James Properties Limited | Construction | 1997 |