| Influence Foundation | Professional & scientific | 2024 |
| Info Security Limited | Wholesale & retail | 2020 |
| Ingenium Automation Limited | Professional & scientific | 2014 |
| Initiative for Conscious AI CIC | Education | 2025 |
| INK and Air Productions Ltd | Information & communication | 2014 |
| Inkcolour UK Ltd | Wholesale & retail | 2013 |
| Innate Change CIC | Other services | 2021 |
| Inner Reality Ltd | Information & communication | 2021 |
| Innocent Collective Ltd | Professional & scientific | 2026 |
| INS & Outs of Ascot Limited | Professional & scientific | 2007 |
| Insha Trading Ltd | Wholesale & retail | 2022 |
| Insight Leads Ltd | Professional & scientific | 2015 |
| Insite Managed Services Limited | Administrative & support | 1999 |
| Instant Recognition Limited | Administrative & support | 1996 |
| Insync Investments Ltd | Real estate | 2025 |
| Integra Financial Services Ltd | Administrative & support | 2007 |
| Integrated Food Projects Limited | Professional & scientific | 2003 |
| Integritas Prima Ltd | Professional & scientific | 2013 |
| INTERNETSHOP2012 Ltd | Information & communication | 2012 |
| Internorm Windows UK Limited | Wholesale & retail | 2007 |
| Interpark (UK) Ltd | Real estate | 2008 |
| Intuitive by Design Ltd | Professional & scientific | 2012 |
| Intuitive Logic Limited | Professional & scientific | 2025 |
| Inventory Agents Property Services Ltd | Real estate | 2018 |
| Investment Management Services Limited | Extraterritorial | 2015 |
| Invogue Limited | Wholesale & retail | 2008 |
| IO Clinical Ltd | Administrative & support | 2019 |
| Io-Co IP Limited | Professional & scientific | 2017 |
| IOK Ltd | Wholesale & retail | 2022 |
| Iota Managed Services Ltd | Professional & scientific | 2014 |
| IOW Rainbow Ltd | Health & social care | 2015 |
| Ipolo Limited | Arts & recreation | 2017 |
| Irish Rose Homes Limited | Real estate | 2025 |
| Irish Rose Interiors Ltd | Real estate | 2024 |
| Irrigate & Thrive Limited | Administrative & support | 2021 |
| Isabelle MAY Limited | Information & communication | 2014 |
| It's ALL Made UP Productions Ltd | Information & communication | 2022 |
| Ithaca Property Ltd | Real estate | 2026 |
| J & B Maintenance Services Limited | Construction | 2013 |
| J & J Wall Limited | Construction | 2011 |
| J a Gilbert Property Services Limited | Construction | 2022 |
| J Hanson Properties Ltd | Real estate | 2024 |
| J Malone Services Ltd | Other services | 2014 |
| J&G Carpenters Ltd | Manufacturing | 2020 |
| J.M.P Electrics Ltd | Manufacturing | 2022 |
| J.T.R Locations Limited | Information & communication | 2018 |
| Jacara International Ltd | Professional & scientific | 2026 |
| Jacksons Accountants (Ascot) Limited | Professional & scientific | 2012 |
| Jacob's Well Developments Limited | Construction | 2006 |
| Jacobs Investments Ltd | Real estate | 2026 |
| Jacost Ltd | Wholesale & retail | 2020 |
| Jacqueline Interiors Limited | Other services | 2013 |
| JAG Dharan Ltd | Administrative & support | 2026 |
| JAI AB Ltd | Hospitality | 2021 |
| Jaijo Limited | Information & communication | 2010 |
| James Heron Property Consultancy Limited | Real estate | 2019 |
| James-Martin & SON Limited | Information & communication | 2014 |
| Jammy Smears Ltd | Information & communication | 2025 |
| JAN DE NUL (UK) Limited | Construction | 1987 |
| Janta Ltd | Professional & scientific | 2025 |
| Jasmine Silk Limited | Manufacturing | 2008 |
| Java Investments Limited | Financial services | 2019 |
| JAY GEE Autos Limited | Wholesale & retail | 2014 |
| Jaytee Training & Development Ltd | Professional & scientific | 2001 |
| JB Consultancy (Wentworth) Limited | Other services | 2018 |
| JC Legal Consultancy Services Limited | Professional & scientific | 2024 |
| JCS Construction Ltd | Construction | 2023 |
| JD & Co Limited | Other services | 2011 |
| JD Chauffeurs Ltd | Transport & logistics | 2024 |
| JD Ventures (London) Limited | Professional & scientific | 2019 |
| JDD Kasaska Ltd | Financial services | 2016 |
| JDI Building Services Ltd | Construction | 2010 |
| Jeeves and Wooster Limited | Administrative & support | 2017 |
| Jehan Limited | Real estate | 2021 |
| JEM Electrical Contracting Ltd | Manufacturing | 2017 |
| JEM15 Limited | Hospitality | 2015 |
| Jepso Ltd | Information & communication | 2013 |
| JFC Group Ltd | Professional & scientific | 2025 |
| JH Wakefield Ltd | Information & communication | 2024 |
| JJT Solutions Ltd | Real estate | 2019 |
| Jlma PR & Business Advisors Limited | Professional & scientific | 2024 |
| Jlmcon Ltd | Construction | 2021 |
| JLP Consultants Ltd | Professional & scientific | 2024 |
| Jlpc Limited | Real estate | 2007 |
| JLS Grab Hire Ltd. | Extraterritorial | 2011 |
| JM & Sons Car Sales Ltd | Wholesale & retail | 2019 |
| JM Advisory Services Limited | Hospitality | 2022 |
| JM and Sons Car Group Ltd | Wholesale & retail | 2025 |
| JMB Strategic Ltd | Professional & scientific | 2025 |
| JMG Fleet Support Ltd | Wholesale & retail | 2023 |
| JML Consulting Group Limited | Information & communication | 2025 |
| JMS Advisors Ltd | Financial services | 2023 |
| JNL Accounting Limited | Professional & scientific | 2019 |
| JO Berman Marketing Limited | Professional & scientific | 2023 |
| Joanna Parsons Counselling & Psychotherapy Limited | Health & social care | 2025 |
| John Molter Consulting Limited | Administrative & support | 2013 |
| John Walliker Consulting Limited | Professional & scientific | 1999 |
| Johnson Advisory Limited | Professional & scientific | 2011 |
| Johnson Residential Ltd | Real estate | 2016 |
| Johnson T Ltd | Professional & scientific | 2025 |