| J&J Mechanics Limited | Wholesale & retail | 2026 |
| J&Y's Properties Limited | Real estate | 2018 |
| J&Y’S Developments Ltd | Real estate | 2024 |
| J.H. Murphy Plastering Contractor Limited | Construction | 1998 |
| J.I.S. Ltd | Manufacturing | 1982 |
| J2H Consultancy Limited | Information & communication | 2013 |
| JA Data Services Limited | Information & communication | 2013 |
| JAB UK Services Ltd | Administrative & support | 2026 |
| Jack Court Management Company Limited | Households | 2004 |
| Jack Solutions Limited | Information & communication | 2022 |
| Jaffa & Jaffa (Holdings) Limited | Professional & scientific | 2021 |
| JAG Machinery Limited | Wholesale & retail | 2008 |
| JAG Property Ventures Ltd | Real estate | 2025 |
| Jaipal Properties Ltd | Real estate | 2025 |
| Jakoless Limited | Professional & scientific | 2022 |
| Jama Carpentry Ltd | Construction | 2025 |
| James House Apartments Ltd | Real estate | 2024 |
| James Martin Investments Limited | Real estate | 2014 |
| James Mcmenamin Engineering Ltd | Construction | 2016 |
| James Noyce & Sons Ltd | Arts & recreation | 2024 |
| Jamie and Kerri Hospitality Ltd | Hospitality | 2025 |
| Jamie Ransom Sound Ltd. | Arts & recreation | 2011 |
| Janet Clare Ltd | Wholesale & retail | 2015 |
| Jarchitecture Ltd | Professional & scientific | 2022 |
| Jared Engineering Ltd | Professional & scientific | 2010 |
| JAS PVT Ltd | Wholesale & retail | 2026 |
| Jason Ralph-Smith Associates Limited | Real estate | 2014 |
| Jassim Financial Solutions Ltd | Professional & scientific | 2025 |
| Jaystack Ltd | Information & communication | 2020 |
| Jazzbuild Ltd | Construction | 2021 |
| JB Paving & Groundworks Ltd | Construction | 2022 |
| JCA Recycling Limited | Construction | 2020 |
| Jclm Events Ltd | Arts & recreation | 2024 |
| JCM Personal Training Ltd | Arts & recreation | 2025 |
| Jcrspropertysourcing Ltd | Real estate | 2026 |
| JD Electrical Solutions Limited | Construction | 2003 |
| JD Printing Services Limited | Other services | 2022 |
| JD Sweeney Training Ltd | Education | 2010 |
| JDM Roofing and Construction Ltd | Construction | 2025 |
| Jdmaintenance Limited | Administrative & support | 2022 |
| Jdmp Limited | Education | 2013 |
| JDN Construction Ltd | Construction | 2022 |
| Jeet Management Consulting Ltd | Professional & scientific | 2022 |
| Jema Properties Ltd | Construction | 2004 |
| Jenoptik Traffic Solutions UK Ltd | Professional & scientific | 1998 |
| Jenoptik UK Limited | Professional & scientific | 2009 |
| Jensen SCM Services Ltd | Professional & scientific | 2021 |
| JEO Europe Holdings Limited | Professional & scientific | 2013 |
| Jessica Bruno Ltd | Professional & scientific | 2024 |
| JET CEE Ltd | Health & social care | 2025 |
| Jet-Talk Limited | Information & communication | 2018 |
| Jetadrain Ltd | Administrative & support | 2002 |
| Jetdrops UK Limited | Professional & scientific | 2025 |
| Jeter Ltd | Arts & recreation | 2017 |
| Jetstream.Uk Ltd | Wholesale & retail | 2007 |
| JG Block Management Limited | Real estate | 2015 |
| JH Property Ltd | Real estate | 2017 |
| JH Site Services Ltd | Construction | 2025 |
| JIA Cleaning Services Ltd | Administrative & support | 2022 |
| Jiayi International Commercial Investment Limited | Wholesale & retail | 2016 |
| JIB Glass Services Limited | Construction | 2011 |
| Jihr Ltd | Professional & scientific | 2025 |
| Jilemjo Consulting Limited | Education | 2015 |
| JJ Carpets Limited | Construction | 2024 |
| JJJ Aviation Limited | Transport & logistics | 2014 |
| JK Coaching Ltd | Professional & scientific | 2023 |
| JK Gregory LLP | | 2011 |
| Jkbm Ltd | Construction | 2026 |
| JKG Windows and Doors Ltd | Construction | 2011 |
| Jklm Realty Ltd | Real estate | 2022 |
| JLC Construction & Maintenance Ltd | Construction | 2024 |
| JLC Property Construction Limited | Administrative & support | 2017 |
| JM Electrical Engineering Ltd | Construction | 2025 |
| JMC UK Properties Limited | Households | 2020 |
| Jmmp Consulting Engineers Ltd | Professional & scientific | 2019 |
| Jmp&H Transport Ltd | Transport & logistics | 2018 |
| JNW Properties LLP | | 2009 |
| JO Ross Events Ltd | Professional & scientific | 2018 |
| Joanna Thornton Coaching Ltd | Health & social care | 2021 |
| Jobsters Inc Ltd | Administrative & support | 2009 |
| John Carpenter Electrical Limited | Construction | 2013 |
| John Cooper Garages Limited | Wholesale & retail | 1965 |
| John Cooper Works Limited | Wholesale & retail | 2002 |
| John Eliot Group Limited | Professional & scientific | 2004 |
| John the Plumb Ltd | Construction | 2016 |
| Johnstone & Johnstone Engineering Limited | Construction | 2019 |
| Jointing and Cable Laying Services Ltd | Construction | 2022 |
| Joneard Ltd | Wholesale & retail | 2025 |
| Joseph and SON Property Maintenance Limited | Construction | 2014 |
| Joubert Projects Ltd | Manufacturing | 2018 |
| Joy Psychology Ltd | Education | 2023 |
| JP and AB Property Limited | Real estate | 2023 |
| JP LED Limited | Manufacturing | 2013 |
| JPG Hotels Limited | Hospitality | 2019 |
| Jphk Restaurants Ltd | Hospitality | 2019 |
| JR Cars Bracknell Ltd | Wholesale & retail | 2021 |
| JR Electrical Contracting Ltd | Construction | 2021 |
| Jr's Kitchen Ltd | Hospitality | 2017 |
| JRC Physio Ltd | Health & social care | 2023 |
| JRI Deals Ltd | Administrative & support | 2020 |