| Itso Limited | Transport & logistics | 2000 |
| Itville Limited | Hospitality | 2013 |
| It’S a Good Choice Ltd | Professional & scientific | 2025 |
| Iuni Limited | Professional & scientific | 2024 |
| Iuvo Property Holdings Ltd | Real estate | 2019 |
| IV Thirteen Ltd | Arts & recreation | 2025 |
| Ivan Klass Limited | Information & communication | 2016 |
| Ivan Plumbing & Heating Ltd | Construction | 2018 |
| Ivernia Plumbing and Heating Limited | Construction | 2023 |
| Ivory Dental Ltd | Health & social care | 2024 |
| Ivory Solace Ltd | Health & social care | 2020 |
| Ivorycare Home Ltd | Health & social care | 2024 |
| Ivsc Recruitment Services Ltd | Administrative & support | 2021 |
| IVY House Environmental Ltd | Professional & scientific | 2006 |
| IVY Lane Venture Ltd | Wholesale & retail | 2022 |
| IVY Limited | Information & communication | 1990 |
| Ivybridgeco Limited | Other services | 2024 |
| Ivyhex Ltd | Information & communication | 2025 |
| IW Tape & Joint Ltd | Construction | 2012 |
| Iwebron Limited | Information & communication | 2023 |
| Iwin Careers Ltd | Professional & scientific | 2026 |
| Iwin Consulting Limited | Professional & scientific | 2025 |
| IXI Labs Ltd | Information & communication | 2021 |
| Ixion Brands Limited | Wholesale & retail | 2020 |
| IXL Events Limited | Hospitality | 2013 |
| Ixora Bloom Limited | Other services | 2023 |
| IYE Limited | Transport & logistics | 2018 |
| Iykepeace Limited | Transport & logistics | 2016 |
| Iyla Beauty Enterprises Limited | Wholesale & retail | 2023 |
| Izakaya Benefits Ltd | Professional & scientific | 2025 |
| Izmir Group of Companies (U.K) Ltd. | Wholesale & retail | 2020 |
| Izzat Modest House Limited | Professional & scientific | 2015 |
| Izzomac Financial Limited | Financial services | 2022 |
| J & G Global Limited | Administrative & support | 2011 |
| J & J Planning and Design Ltd | Professional & scientific | 2025 |
| J & M TM Ltd | Construction | 2024 |
| J & R Enterprises Ltd | Wholesale & retail | 2022 |
| J & S Precision Engineering Limited | Manufacturing | 1989 |
| J & T Herbert Loft Conversions Ltd | Construction | 2023 |
| J and R Workplaces Limited | Real estate | 2021 |
| J and S Tyres Brakes and Suspension Ltd | Professional & scientific | 2025 |
| J B Sons Ltd | Wholesale & retail | 2017 |
| J Bamforth Limited | Transport & logistics | 2018 |
| J C Ductwork Limited | Construction | 2002 |
| J D Automotive Limited | Wholesale & retail | 2014 |
| J D L Marketing Ltd | Administrative & support | 2026 |
| J E Carley Ltd | Financial services | 2025 |
| J E Goodman Limited | Water & waste | 2003 |
| J F Agricultural Engineering Limited | Manufacturing | 2010 |
| J F Car Delivery Ltd | Transport & logistics | 2026 |
| J Future Group Ltd | Construction | 2023 |
| J G Contractors Limited | Construction | 2006 |
| J Gayler Services Limited | Manufacturing | 2022 |
| J Hagan Limited | Health & social care | 2023 |
| J Hart Building Ltd | Other services | 2017 |
| J Heebink (UK) Limited | Transport & logistics | 1983 |
| J K Leisure Group Limited | Financial services | 2024 |
| J Kane Plasterers Ltd | Construction | 2022 |
| J L Coatings & Repairs Specialists Ltd | Construction | 2025 |
| J L N Inventories Limited | Professional & scientific | 2025 |
| J Moodie Roofing Ltd | Construction | 2025 |
| J Oral Care Limited | Health & social care | 2016 |
| J R Vegetarian Ltd | Wholesale & retail | 2007 |
| J R Westcotts Ltd | Wholesale & retail | 2013 |
| J Richardson Ltd | Financial services | 2016 |
| J S a Consultants Limited | Information & communication | 1992 |
| J S Industries Limited | Administrative & support | 2014 |
| J S J Property Rentals Limited | Real estate | 2023 |
| J S J Roofing Ltd | Construction | 2003 |
| J S Sales Agency Limited | Professional & scientific | 2012 |
| J S Technical Food Solutions Ltd | Professional & scientific | 2017 |
| J System Solutions Limited | Information & communication | 2005 |
| J T Property Services Limited | Construction | 2008 |
| J V B S Associates Limited | Information & communication | 2010 |
| J&B Sports Ltd | Arts & recreation | 2025 |
| J&H Assessments Limited | Professional & scientific | 2012 |
| J&H Shanahan Holdings Ltd | Professional & scientific | 2023 |
| J&J Decorating & Maintenance Ltd | Construction | 2021 |
| J&J Realty Investments Limited | Real estate | 2025 |
| J&J Worldwide Services Limited | Manufacturing | 2020 |
| J&J's Barbershop Limited | Other services | 2024 |
| J&K Courier Services Ltd | Transport & logistics | 2021 |
| J&L Commins Property Ltd | Hospitality | 2026 |
| J&M Property Ltd | Real estate | 2026 |
| J&M Property Rentals Limited | Real estate | 2019 |
| J&M Provisions PVT Ltd | Wholesale & retail | 2018 |
| J&N Mano Ltd | Health & social care | 2021 |
| J&S Webb Properties Ltd | Construction | 2024 |
| J-Bucks Next GEN Ltd | Arts & recreation | 2024 |
| J-First Recruitment Limited | Information & communication | 2002 |
| J. D. Audio Ltd | Arts & recreation | 2016 |
| J. Dolton Plumbers Ltd | Construction | 2024 |
| J. M. Page (Plumbing & Heating Engineers) Limited | Construction | 2003 |
| J. M. Page Limited | Construction | 2008 |
| J. T. M. a Ltd | Health & social care | 2025 |
| J. Tonna & Co Limited | Professional & scientific | 1998 |
| J.A.C Consultancy Ltd | Information & communication | 2024 |
| J.A.J. Sawbridge & Sons Limited | Agriculture & fishing | 1983 |
| J.D.L Rail Solutions Limited | Manufacturing | 2018 |
| J.E.T Construction (Milton Keynes) Limited | Construction | 1998 |