| Isiya Ltd | Information & communication | 2024 |
| Isla Casa Limited | Real estate | 2016 |
| Islamifyacademy Ltd | Education | 2023 |
| Island Cove Group Limited | Construction | 2025 |
| Island Mortgages Ltd | Financial services | 2017 |
| Isle 74 Ltd | Manufacturing | 2025 |
| Isleworth Enterprises Limited | Real estate | 2006 |
| ISM Education Limited | Education | 1994 |
| ISM Electrical Ltd | Energy | 2022 |
| Ismb Properties Ltd | Real estate | 2019 |
| Isobel Child Associates Ltd | Education | 2017 |
| Isobel House Limited | Households | 1989 |
| Isome Limited | Professional & scientific | 2015 |
| Ison Nursing Agency and Care Services Limited | Administrative & support | 2010 |
| Isotope JSC Limited | Manufacturing | 2025 |
| Ispectronic Services Limited | Manufacturing | 2016 |
| Ispeed London Ltd | Information & communication | 2014 |
| Issac Harson Consulting Ltd | Administrative & support | 2017 |
| IST Security Ltd | Other services | 2023 |
| IST Step Limited | Information & communication | 2024 |
| Istanaliving Ltd | Households | 2026 |
| Isufi Property Limited | Real estate | 2024 |
| Isurika Properties Ltd | Real estate | 2025 |
| IT & Comms Group Ltd | Information & communication | 2019 |
| IT Design Digital Ltd | Information & communication | 2025 |
| IT Fieldfy Ltd | Information & communication | 2022 |
| IT Global HR Solutions Ltd | Administrative & support | 2018 |
| IT Skills Ltd | Information & communication | 2022 |
| IT Techno Plus Limited | Information & communication | 2012 |
| IT Techs Limited | Information & communication | 2014 |
| IT View Consulting Ltd | Information & communication | 2008 |
| IT World Limited | Information & communication | 2015 |
| It's NOT 1998 Ltd | Financial services | 2020 |
| It's NOT 1999 Ltd | Information & communication | 2020 |
| Italian Living International Limited | Wholesale & retail | 2018 |
| Italian Living London Limited | Wholesale & retail | 2005 |
| Italiyadrycleaning Limited | Wholesale & retail | 2024 |
| Italsav Limited | Wholesale & retail | 2023 |
| Itavengers Ltd | Information & communication | 2022 |
| Itch Series Ltd | Information & communication | 2025 |
| ITE Smartcity (UK) Limited | Financial services | 2021 |
| Itechhub Consultancy Limited | Real estate | 2014 |
| Itecho Ltd | Other services | 2025 |
| Itenna Holdings Limited | Information & communication | 2012 |
| Itenna Limited | Information & communication | 2012 |
| Itiah Ltd | Professional & scientific | 2018 |
| Itop-P Ltd | Wholesale & retail | 2010 |
| Itrac Holdings Limited | Administrative & support | 2024 |
| Itrac Solutions Ltd | Information & communication | 2017 |
| ITS (U.K.) Limited | Manufacturing | 1988 |
| ITS Group Holdings Limited | Professional & scientific | 2021 |
| ITS Limousines UK Limited | Transport & logistics | 2012 |
| Itscricket Limited | Wholesale & retail | 2017 |
| Itsolve Solutions Ltd | Information & communication | 2018 |
| Itwiza Limited | Other services | 2018 |
| Iusmar Logistics Ltd | Transport & logistics | 2018 |
| Iuvo Ingenii Ltd | Transport & logistics | 2018 |
| IV Property Development Limited | Construction | 2015 |
| IV Tiling Ltd | Construction | 2021 |
| IV17 Interiors Ltd | Construction | 2020 |
| Ivan Costel Limited | Construction | 2017 |
| Ivan Geni Ltd | Health & social care | 2021 |
| Iveson Consultancy Limited | Information & communication | 1997 |
| Iveson Properties LLP | | 2007 |
| Ivich Co Ltd | Administrative & support | 2019 |
| IVL Utilities Ltd | Construction | 2022 |
| Ivopro Ltd | Administrative & support | 2025 |
| Ivory Film Limited | Information & communication | 2021 |
| IVR3T Co Ltd | Wholesale & retail | 2026 |
| IVY Blenheim Ltd | Financial services | 2025 |
| IVY Care Management Limited | Transport & logistics | 2026 |
| IVY Homes Group Ltd | Real estate | 2025 |
| IVY LI Limited | Hospitality | 2016 |
| Iyer Consulting Limited | Professional & scientific | 2014 |
| Iyki Ltd | Information & communication | 2024 |
| Iysa Interior Ltd | Wholesale & retail | 2025 |
| Iyve Ltd | Construction | 2023 |
| IZ Contractors Ltd | Construction | 2011 |
| Izzyblue Limited | Wholesale & retail | 2024 |
| J $ K Properties Limited | Real estate | 2017 |
| J & a Capital Partners Limited | Real estate | 2025 |
| J & a Group Holdings Limited | Financial services | 2022 |
| J & a London Properties Ltd | Real estate | 2018 |
| J & a Properties (UK) Limited | Real estate | 2004 |
| J & a Property Holdings LLP | | 2021 |
| J & B UK Investments Limited | Construction | 2016 |
| J & D Manta Limited | Real estate | 2008 |
| J & G Investments Limited | Financial services | 2019 |
| J & H Partners Ltd | Real estate | 2017 |
| J & J Express Limited | Wholesale & retail | 2017 |
| J & M Michaels Limited | Wholesale & retail | 2008 |
| J & M Resurfacing Limited | Construction | 2003 |
| J & R Medical Limited | Health & social care | 2014 |
| J & S Properties (London) Limited | Real estate | 2020 |
| J & S Properties Investment Limited | Real estate | 2014 |
| J a & Brown Ltd | Other services | 2019 |
| J and S Brothers Ltd | Real estate | 2020 |
| J B Patrol Ltd | Professional & scientific | 2022 |
| J Bear Properties Limited | Real estate | 2016 |
| J Bejan Construction Ltd | Construction | 2023 |