| It&Sm Solutions Ltd | Information & communication | 2024 |
| Italdent Limited | Health & social care | 2015 |
| Itelco Private Limited | Wholesale & retail | 2010 |
| Itew Ltd | Information & communication | 2025 |
| Itosyncrasies Ltd | Information & communication | 2020 |
| ITS Your Day Limited | Professional & scientific | 2004 |
| ITT Datacommunications Limited | Professional & scientific | 1963 |
| ITT Industries Holdings Limited | Financial services | 2011 |
| ITT Industries Limited | Manufacturing | 1964 |
| Ivone Bostan Services Ltd | Construction | 2015 |
| Ivory Nation Investments Ltd | Financial services | 2023 |
| IVS Venture Limited | Transport & logistics | 2017 |
| IVY CB Productions Ltd | Information & communication | 2024 |
| IX Home Limited | Construction | 2009 |
| J and E Flooring Limited | Construction | 2014 |
| J C Beale Brickwork Limited | Construction | 1995 |
| J Goddard Groundworks Limited | Administrative & support | 2013 |
| J Harris Electrical Ltd | Construction | 2016 |
| J L Scaffolding Limited | Construction | 2012 |
| J M Golf Ltd | Wholesale & retail | 2025 |
| J N Treescape Ltd | Agriculture & fishing | 2017 |
| J Owen Medical Limited | Health & social care | 2017 |
| J&M Building Services Ltd | Construction | 2022 |
| J. Reed Psychology Limited | Administrative & support | 2004 |
| J.A Tech Services Ltd | Construction | 2023 |
| J.A.G. Environmental Partnership Limited | Professional & scientific | 1992 |
| J.B.Philp & SON Limited | Wholesale & retail | 1960 |
| J.E.M.J. LLP | | 2011 |
| J.H & E.K Limited | Real estate | 2018 |
| J.L.D. Construction Ltd | Construction | 2017 |
| J.W.Farmer and Sons Ltd | Construction | 2008 |
| JAC Electrical Systems Ltd | Construction | 2023 |
| Jacek & Dorota Ltd. | Transport & logistics | 2014 |
| Jacek GIL Limited | Transport & logistics | 2017 |
| Jackson Wright Property Ltd | Real estate | 2022 |
| Jackson's Unique Mineral Processing Services Limited | Professional & scientific | 2018 |
| Jacobs Barbers Basingstoke Ltd | Other services | 2023 |
| Jacobs Properties Sales and Lettings Ltd | Real estate | 1999 |
| Jacquie Chart Holdings Limited | Financial services | 2020 |
| Jada Medical Limited | Health & social care | 2024 |
| Jada Stores Limited | Wholesale & retail | 2026 |
| Jaeger Medical UK Limited | Health & social care | 1985 |
| Jagat Janani Limited | Real estate | 2022 |
| Jagdeep Ltd | Transport & logistics | 2026 |
| JAI Pharma Limited | Manufacturing | 2012 |
| JAI Shree Mahakal.Co Ltd | Hospitality | 2025 |
| Jake Pitney Consulting Limited | Professional & scientific | 2026 |
| Jakub Dudka Logistics Limited | Transport & logistics | 2014 |
| Jalj Consulting Limited | Professional & scientific | 2025 |
| James Knight Interiors Ltd | Manufacturing | 2021 |
| James Magner Consulting Ltd | Administrative & support | 2024 |
| Janaway Farms Limited | Agriculture & fishing | 1979 |
| Jandatech Trading Ltd | Wholesale & retail | 2025 |
| Jane Skingley Art Limited | Arts & recreation | 2017 |
| Janjan Property Management Limited | Real estate | 2017 |
| Janna Housing Ltd | Real estate | 2023 |
| Janus Software & Consultancy Services Ltd | Information & communication | 2026 |
| Januz Holdings Ltd | Professional & scientific | 2020 |
| Janyx Ltd | Information & communication | 2010 |
| JAR Enterprise Holdings Ltd | Financial services | 2025 |
| Jarona Consulting Limited | Other services | 2017 |
| Jasmine Buildings Limited | Real estate | 2024 |
| Jasmine June Productions Limited | Arts & recreation | 2005 |
| Jasmine Properties Investment Limited | Construction | 2024 |
| Jason P Ward Ltd | Information & communication | 2015 |
| Jathedar Consulting Limited | Information & communication | 2022 |
| Javani Ltd | Wholesale & retail | 2019 |
| JAW Plumbing & Heating Ltd | Construction | 2024 |
| Jayes Estates Limited | Real estate | 2026 |
| Jayess Assets Limited | Real estate | 2004 |
| Jaynemesis Capital Ltd | Professional & scientific | 2021 |
| Jayrag Worldwide PVT Ltd | Transport & logistics | 2025 |
| Jays Accountants & Tax Advisors LLP | | 2014 |
| Jays Tax Advisors Ltd | Extraterritorial | 2014 |
| JB & SJ Ltd | Hospitality | 2018 |
| JB Architectural Consultancy Ltd | Other services | 2025 |
| JB Building & Carpentry Hampshire Ltd | Construction | 2016 |
| JB Environmental Limited | Professional & scientific | 2008 |
| JB Nordic Limited | Professional & scientific | 2009 |
| JB Survey Limited | Administrative & support | 1989 |
| Jb-Av Installations Limited | Manufacturing | 2017 |
| JBN Personnel Limited | Administrative & support | 2022 |
| Jbpm Online Limited | Professional & scientific | 2009 |
| JBW Creative Holdings Limited | Financial services | 2023 |
| JC Naval Consulting Limited | Professional & scientific | 2025 |
| Jc's Barbers Limited | Other services | 2014 |
| JD Consulting Services UK Ltd | Information & communication | 2020 |
| JDK Business Solutions Limited | Professional & scientific | 2022 |
| JDL Sports Rehabilitation Ltd | Arts & recreation | 2025 |
| JDR Floors Ltd | Construction | 2024 |
| JE Group (Holdings) Limited | Financial services | 2016 |
| JE Group Limited | Wholesale & retail | 2009 |
| Jeacos Consulting Ltd | Professional & scientific | 2023 |
| JEB Management Consulting Limited | Professional & scientific | 2015 |
| Jehovah Nissi Ltd | Real estate | 2022 |
| JEM Promotions UK Limited | Professional & scientific | 2001 |
| Jenny Grey Consulting Limited | Professional & scientific | 2025 |
| Jensomakes Ltd | Manufacturing | 2025 |
| Jeremy Bailey CBE Ltd | Arts & recreation | 2025 |
| Jeremy Bailey Consulting Limited | Information & communication | 2025 |