| Immunointelligence Ltd | Professional & scientific | 2025 |
| Impact Lighting Design Services Ltd | Professional & scientific | 2017 |
| Impact Lighting Solutions Limited | Construction | 2013 |
| Impossible Digital Ltd | Information & communication | 2013 |
| Impossible Factual Limited | Information & communication | 2006 |
| Impulse Research Ltd | Information & communication | 2024 |
| IN Black and White Consulting Ltd | Professional & scientific | 2025 |
| IN My Zone Limited | Arts & recreation | 2020 |
| Incight Ltd | Professional & scientific | 2017 |
| Indigo Mortgage and Financial Services Ltd | Financial services | 2018 |
| Indus ARC Limited | Real estate | 2023 |
| Inelxia Limited | Professional & scientific | 2013 |
| Infineum International Limited | Manufacturing | 1998 |
| Infineum UK Ltd. | Manufacturing | 1995 |
| Infineum UK Pension Trustee Ltd | Financial services | 1998 |
| Infinitesima Limited | Manufacturing | 2001 |
| Infinnovation Limited | Manufacturing | 2013 |
| Inhurst Landscapes Limited | Administrative & support | 2014 |
| Inition Energy Ltd | Manufacturing | 2021 |
| Injun Ltd | Wholesale & retail | 2024 |
| Inklusiv Creative Agency Ltd | Professional & scientific | 2020 |
| Inkunzi Consulting Limited | Administrative & support | 2012 |
| Inmotion Studios Limited | Arts & recreation | 2017 |
| Innovius Technologies Ltd | Information & communication | 2016 |
| Inovatrix Ltd | Wholesale & retail | 2024 |
| Inpictura Limited | Administrative & support | 2022 |
| Insight Science Limited | Professional & scientific | 2014 |
| Insightful Strategies Ltd | Professional & scientific | 2023 |
| Integrate AI Works Ltd | Information & communication | 2026 |
| Integrated Project Systems Limited | Information & communication | 1993 |
| Integrit HE Ltd | Professional & scientific | 2023 |
| Integrity Data Science Ltd | Professional & scientific | 2022 |
| Integrity Homes and Lettings Limited | Real estate | 2020 |
| Inter Construction Services Ltd | Construction | 2024 |
| Inter Metal & Scrap Ltd | Water & waste | 2024 |
| Interact Psychology Ltd | Health & social care | 2024 |
| Intergalactic Cat Company Ltd | Arts & recreation | 2023 |
| Intermed Limited | Manufacturing | 2007 |
| International College Portsmouth Ltd. | Education | 2008 |
| International College Wales Limited | Financial services | 2007 |
| International Equipment Group Ltd | Administrative & support | 2013 |
| Intralink Group Limited | Professional & scientific | 2011 |
| Intralink Limited | Professional & scientific | 1989 |
| Invention Development Ltd | Information & communication | 2018 |
| Investassure Limited | Professional & scientific | 2012 |
| Invincible Software Holdings Ltd | Information & communication | 2023 |
| Inviting Retreats Ltd | Real estate | 2026 |
| Inzent Limited | Real estate | 2012 |
| ION Opticks UK Holdings Limited | Financial services | 2025 |
| ION Opticks UK Limited | Professional & scientific | 2025 |
| Iponly Ltd | Professional & scientific | 2024 |
| IR Construction Services Ltd | Construction | 2009 |
| Irenic Home Limited | Information & communication | 2026 |
| Irodev Ltd | Wholesale & retail | 2024 |
| Ironman Ltd. | Arts & recreation | 2009 |
| Isabel TEO Plastic Surgery Ltd | Health & social care | 2024 |
| Iscream Oxford Limited | Real estate | 2014 |
| Iseedea Limited | Professional & scientific | 2012 |
| Isis Court Management Limited | Administrative & support | 2004 |
| Ismail Lawal. Limited | Health & social care | 2017 |
| Isnia Technologies Ltd. | Information & communication | 2024 |
| Istaffhub Limited | Information & communication | 2019 |
| IT Inspires Ltd | Information & communication | 2012 |
| IT Won'T Cost the Earth Ltd | Wholesale & retail | 2019 |
| Itml Ltd | Professional & scientific | 2013 |
| Ivan Kilbee Heating Limited | Construction | 2002 |
| J & K Adamberry Limited | Real estate | 2023 |
| J a Plumbing and Heating Solutions Limited | Construction | 2022 |
| J C Motorwise Limited | Wholesale & retail | 2011 |
| J Campion Development Limited | Professional & scientific | 2024 |
| J D P Interiors Ltd | Professional & scientific | 2025 |
| J International Consulting Limited | Professional & scientific | 2025 |
| J K Garden Maintenance Limited | Administrative & support | 2008 |
| J P Mcgrath Bloodstock Limited | Arts & recreation | 2017 |
| J Perry Environmental Consulting Ltd | Professional & scientific | 2025 |
| J Pincombe Medical Services Ltd | Health & social care | 2025 |
| J W Srawley Ltd | Information & communication | 2023 |
| J&A Bacon Limited | Real estate | 2017 |
| J&G Lotus Trading Ltd | Hospitality | 2024 |
| J&S House of Design Limited | Construction | 2014 |
| J'S Sports Bar Bicester Ltd | Hospitality | 2025 |
| J, Curtis & Sons Limited | Real estate | 1948 |
| J. Bowers Holding Ltd | Professional & scientific | 2025 |
| J. Curtis & Sons (Holdings) Limited | Professional & scientific | 2012 |
| J. Spratley - Architect Ltd | Real estate | 2025 |
| Jack & Jill Day Nursery Ltd | Education | 2003 |
| Jack Pijl Psychotherapy Ltd | Health & social care | 2024 |
| Jackson IT Limited | Information & communication | 2017 |
| Jacling Accountancy Ltd | Professional & scientific | 2024 |
| Jacmo Limited | Information & communication | 2022 |
| JAG Civils Limited | Construction | 2017 |
| JAG Oxford Limited | Wholesale & retail | 2024 |
| Jals Auto Mechs Ltd | Wholesale & retail | 2023 |
| James Best Racing Limited | Arts & recreation | 2017 |
| James Bowen Racing Limited | Arts & recreation | 2025 |
| James Clement Publishing Services Ltd | Information & communication | 2026 |
| James Logan Hall Limited | Professional & scientific | 2013 |
| James Welch Consulting Limited | Information & communication | 2019 |
| Jamie Railton Sales Agency Limited | Arts & recreation | 2014 |
| Jamisaw Capital Limited | Professional & scientific | 2025 |