| Innovative Accountants Ltd | Professional & scientific | 2014 |
| Innsight Solutions Limited | Information & communication | 2026 |
| Inntangled Ltd | Information & communication | 2025 |
| Insight Into Change Ltd | Professional & scientific | 2022 |
| Insightful HR Limited | Administrative & support | 2017 |
| Insights Psychology Limited | Professional & scientific | 2020 |
| Institut DE LA Ville International Limited | Professional & scientific | 2013 |
| Intage Limited | Professional & scientific | 2003 |
| Integrated Behavioural Consultancy Limited | Education | 2017 |
| Integrated Developments (EU) Limited | Professional & scientific | 2004 |
| Inteligenesis Ltd | Manufacturing | 2017 |
| Intellika Limited | Professional & scientific | 2006 |
| Interdesign (UK) Limited | Wholesale & retail | 2000 |
| Intermedium Limited | Administrative & support | 1998 |
| International Media Advertising Limited | Professional & scientific | 1998 |
| International Medical Supplies Ltd | Wholesale & retail | 2020 |
| International VIP Events Limited | Arts & recreation | 2020 |
| Intrabank Data Limited | Information & communication | 1996 |
| Inventia 57 Limited | Manufacturing | 2020 |
| Invicta Contracting Services Limited | Real estate | 2015 |
| Invoke-Uk Ltd | Wholesale & retail | 2025 |
| Invoyage Limited | Administrative & support | 2015 |
| IP65 Systems Ltd | Wholesale & retail | 2015 |
| Ipresent Group Limited | Professional & scientific | 2013 |
| Ipresent Limited | Information & communication | 2012 |
| Ipurangi Limited | Information & communication | 2022 |
| Iraj Jannatie Ataie Literary Foundation Limited | Extraterritorial | 2026 |
| Irena Tyshyna Ltd | Other services | 2018 |
| Irfon River Leisure Parks Limited | Hospitality | 2021 |
| Ironbridge Estates Limited | Construction | 2025 |
| Iseran Capital Limited | Professional & scientific | 2022 |
| ISF Solutions Ltd | Financial services | 2009 |
| ISH International Limited | Education | 2020 |
| Ishrat Sahgal Interiors Ltd | Professional & scientific | 2022 |
| Isla & Amelia Property Limited | Real estate | 2023 |
| ISS Brightspark Limited | Hospitality | 2019 |
| ISS Facility Services Limited | Hospitality | 1966 |
| ISS Mediclean Limited | Hospitality | 1982 |
| ISS Technical Services Corporate Solutions Limited | Administrative & support | 2013 |
| ISS UK Holding Limited | Professional & scientific | 2005 |
| ISS UK Limited | Professional & scientific | 1949 |
| Istek Ltd | Information & communication | 2008 |
| ISV Exit Strategy Limited | Professional & scientific | 2010 |
| IT Courier Ltd | Transport & logistics | 2022 |
| IT Support Desk Limited | Information & communication | 2001 |
| It's for ME Limited | Wholesale & retail | 2010 |
| Italent Ltd | Administrative & support | 2010 |
| Italian Luxury Surfaces Ltd | Construction | 2015 |
| ITSERVICES4.ME Limited | Information & communication | 2018 |
| IUK Holdings Ltd | Financial services | 2020 |
| IVY Homes (London) Limited | Construction | 2006 |
| IW Transport Ltd | Transport & logistics | 2016 |
| Izamoda Limited | Wholesale & retail | 1990 |
| Izycare Company Limited | Administrative & support | 2010 |
| J & G Development Limited | Real estate | 2003 |
| J & S Property Holdings (London) Limited | Construction | 2019 |
| J Brooks Consulting Limited | Professional & scientific | 2024 |
| J E N O Management Limited | Professional & scientific | 2015 |
| J Goulding Consulting Limited | Professional & scientific | 2017 |
| J R Landscaping & Paving Limited | Construction | 2018 |
| J Squared Business Consulting Ltd | Professional & scientific | 2014 |
| J Vincent Roofing Limited | Construction | 2012 |
| J W Keenan Limited | Information & communication | 2014 |
| J&W Consulting Limited | Professional & scientific | 2014 |
| J-Raw Developments Ltd | Real estate | 2019 |
| J. Shepperson Limited | Agriculture & fishing | 1996 |
| J.B Roofing and Guttering Limited | Construction | 2021 |
| J.Paterson (Builders) Limited | Construction | 2005 |
| Jack Williams Car Sales Limited | Wholesale & retail | 2017 |
| Jackson Limes Consulting Limited | Professional & scientific | 2017 |
| Jacob Media Limited | Financial services | 2023 |
| James Barry Associates Limited | Construction | 2006 |
| James Gibbons Format Limited | Manufacturing | 2001 |
| James Gibbons Holdings Limited | Professional & scientific | 1990 |
| James LEE Properties Ltd | Real estate | 2024 |
| James Littlefair Limited | Professional & scientific | 2020 |
| Jamivy Ltd | Real estate | 2025 |
| JAN Leeks Limited | Information & communication | 2008 |
| Jasmine Care Group Limited | Financial services | 2021 |
| Jasmine Care Holdings Limited | Financial services | 2010 |
| JAY KAY Services Limited | Extraterritorial | 2008 |
| Jayne Redmond Bespoke Ltd | Manufacturing | 2025 |
| Jayne Redmond Handmade Limited | Manufacturing | 2016 |
| Jayryn Enterprises Limited | Information & communication | 2025 |
| JB & Ace Limited | Professional & scientific | 2015 |
| JB & Associates Limited | Other services | 2004 |
| JBE Skincare Ltd | Other services | 2023 |
| JC Consultancy Solutions Ltd | Administrative & support | 2016 |
| Jcrd Hospitality Limited | Hospitality | 2026 |
| JCS (FAM) Limited | Real estate | 2015 |
| JD Holistic Bookkeeping Services Limited | Professional & scientific | 2016 |
| Jdbs Ventures Ltd | Arts & recreation | 2025 |
| Jedco Product Designers Ltd. | Professional & scientific | 2002 |
| JEF Properties Limited | Real estate | 2023 |
| Jenkins Associates Search and Selection Ltd | Administrative & support | 2019 |
| Jenkins One Limited | Administrative & support | 2014 |
| Jenks & Cattell Engineering Limited | Manufacturing | 1986 |
| Jenroh Limited | Real estate | 2021 |
| JET Members Ltd | Wholesale & retail | 2023 |
| Jeymash Limited | Real estate | 1992 |