| Inri United Ltd | Other services | 2016 |
| Inrise Limited | Wholesale & retail | 2024 |
| Installerpro Ltd | Information & communication | 2025 |
| Insulation Central Ltd | Construction | 2018 |
| Insvent Limited | Information & communication | 2017 |
| Integrity Tax & Accounting Ltd | Professional & scientific | 2025 |
| Intense Therapies Ltd | Health & social care | 2025 |
| Intergenerational Wealth Management Limited | Administrative & support | 2017 |
| Intradex LLP | | 2017 |
| Intron Ltd | Wholesale & retail | 2019 |
| Investro Projects Ltd | Professional & scientific | 2018 |
| Ionara Ltd | Health & social care | 2026 |
| Irie Security Ltd | Financial services | 2023 |
| IS YOU Limited | Other services | 2016 |
| ISB Consultants Ltd | Professional & scientific | 2021 |
| Island Homes Kent Ltd | Real estate | 2013 |
| ISM 25 Carpentry Ltd | Construction | 2025 |
| Itaar Recruitment Agency Ltd | Administrative & support | 2020 |
| ITF Estates Ltd | Real estate | 2025 |
| IX-01 Limited | Construction | 2025 |
| IXO (Beech Hill) Ltd | Construction | 2019 |
| IXO (Consulting) LLP | | 2020 |
| IXO (Impact) LLP | | 2024 |
| IXO (New River Place) LLP | | 2020 |
| IXO ARC Limited | Real estate | 2024 |
| IXO Group LLP | | 2022 |
| IXO Ltd | Construction | 2017 |
| IXO Tower Hamlets Ltd | Real estate | 2025 |
| IZ Courier Ltd | Wholesale & retail | 2019 |
| Izak James Ltd | Administrative & support | 2017 |
| J & J Properties LLP | | 2012 |
| J and S Property Lettings Limited | Real estate | 2021 |
| J R Executive Cars Ltd | Transport & logistics | 2022 |
| J&M DRY Cleaning Services Ltd | Other services | 2017 |
| J.Edwards Roofing Ltd | Construction | 2022 |
| J.P. Aero-Com Engineering Co. Limited | Wholesale & retail | 1965 |
| J3 Computer Solutions Ltd | Manufacturing | 2020 |
| Jacob Property Investments Limited | Real estate | 2011 |
| Jacs Consultants Ltd | Administrative & support | 2022 |
| Jadistributors Ltd | Wholesale & retail | 2026 |
| Jakova Joinery Limited | Construction | 2012 |
| James Compton Ltd | Information & communication | 2015 |
| James Ellis Coaching Ltd | Health & social care | 2025 |
| James Lewis Collection Limited | Information & communication | 2025 |
| James Saffron Ltd | Administrative & support | 2012 |
| Jane Rees and Co Ltd | Administrative & support | 2018 |
| Jasani Consultancy Limited | Real estate | 2013 |
| Jason Biddle Associates Limited | Real estate | 1998 |
| JB Osteo Fitness Limited | Health & social care | 2025 |
| Jcck Services Limited | Real estate | 2014 |
| JCM Consultants Ltd | Professional & scientific | 2019 |
| JDW Flooring Supplies Limited | Wholesale & retail | 2021 |
| JEN Media TV Ltd | Professional & scientific | 2023 |
| Jeyanney Make UP Services Ltd | Other services | 2020 |
| Jilani Aggregate Ltd | Real estate | 2022 |
| JJ Brand & Creative Consulting Ltd | Professional & scientific | 2022 |
| JK Carpentry and Loft Conversions Ltd | Manufacturing | 2022 |
| JK Elite Electrical Ltd | Manufacturing | 2026 |
| JKL Consultancy Limited | Construction | 2025 |
| JML Maintenance Limited | Construction | 2005 |
| John Price Photography Ltd | Professional & scientific | 1995 |
| John Quality Ltd | Construction | 2023 |
| Johnny Savage Design Ltd | Professional & scientific | 2022 |
| Johnson Consultancy Ltd | Professional & scientific | 2022 |
| Jolartom Properties Limited | Real estate | 1963 |
| Jolly Learning Limited | Manufacturing | 1987 |
| Jolly Pet Sitters Ltd | Other services | 2025 |
| Jones & Jones (Corporate Services) Limited | Information & communication | 1989 |
| Jooed Properties Ltd | Real estate | 2022 |
| Joss Dean Limited | Information & communication | 2025 |
| Joyia Hire Ltd | Transport & logistics | 2019 |
| JPM Consultancy Ltd | Professional & scientific | 2022 |
| JSB Building Contractors Ltd | Construction | 2018 |
| JTA Radiology Limited | Health & social care | 2010 |
| JTC Fire Ltd | Public administration | 2025 |
| Juelo Consult Limited | Professional & scientific | 2018 |
| Juggs Ltd | Wholesale & retail | 2023 |
| JUN CUT Limited | Other services | 2023 |
| Juniper Investment Properties Ltd | Real estate | 2015 |
| Junk Bunk Ltd | Water & waste | 2016 |
| Junk Expert Ltd | Water & waste | 2018 |
| Just Vitos Ltd | Administrative & support | 2017 |
| JY Investments Ltd | Real estate | 2020 |
| K FOX Developments Limited | Construction | 2002 |
| K&A Hayer Ltd | Real estate | 2024 |
| K. K. B Enterprise Ltd | Hospitality | 2025 |
| K3C House Limited | Administrative & support | 2010 |
| K9SAXON Ltd | Public administration | 2026 |
| Kaino Studio Ltd | Administrative & support | 2024 |
| Karl Ward Ltd | Construction | 2016 |
| Kayleighkmua Ltd | Arts & recreation | 2017 |
| KCB Consulting Ltd | Professional & scientific | 2024 |
| Kennard's Ltd | Professional & scientific | 2019 |
| Kerry Savage Ltd | Professional & scientific | 2024 |
| Keyah Muti Essex Limited | Real estate | 2023 |
| Keyah Muti Hampshire Limited | Real estate | 2023 |
| Keyah Muti Ltd | Real estate | 2019 |
| Keyah Muti Sussex Limited | Real estate | 2023 |
| KF Pictures Limited | Professional & scientific | 2024 |
| Kfrw (Westfield) Ltd | Real estate | 2023 |