| Infuse Construction Limited | Construction | 2013 |
| Inglenook Media Ltd | Administrative & support | 2022 |
| Inland U.K Limited | Wholesale & retail | 1987 |
| Innovecture Ltd | Information & communication | 2022 |
| Inpertilent Limited | Information & communication | 2017 |
| Insolvency Dispute Resolution Support Limited | Administrative & support | 2016 |
| Insp!Re Ltd | Education | 2024 |
| Inspire Accounting (UK) Ltd | Professional & scientific | 2020 |
| Insta Associates Ltd | Professional & scientific | 2018 |
| Installations (Ealing) Limited | | 1953 |
| Institute for Independent Business | Professional & scientific | 1994 |
| Institute for Independent Business-International Limited | Education | 2003 |
| Institute of Public Loss Assessors Limited | Other services | 1966 |
| Insurgy Ltd | Real estate | 2018 |
| Integriti Technical Services Limited | Professional & scientific | 2016 |
| Interior Professional Services Limited | Administrative & support | 2008 |
| International Collective IP Ltd | Extraterritorial | 2026 |
| International Collective Limited | Arts & recreation | 2025 |
| Internet Sales Services Limited | Professional & scientific | 2009 |
| Interstellar Associates Ltd | Professional & scientific | 2016 |
| Investihomes Ltd | Real estate | 2023 |
| Invisible Folk Ltd | Arts & recreation | 2018 |
| Iota Land Investments Limited | Administrative & support | 1985 |
| IOW Lettings Ltd | Real estate | 2020 |
| Ipify Limited | Information & communication | 2012 |
| Ipsden LLP | | 2024 |
| Iris Press Limited | Information & communication | 2005 |
| Irving Legal Ltd | Professional & scientific | 2019 |
| Iset Development Ltd | Construction | 2023 |
| Isleworth Developments Limited | Real estate | 2018 |
| ISO Fish and Chips Ltd | Hospitality | 2025 |
| IT Data Solutions Limited | Information & communication | 2014 |
| IT Mighty Ltd | Information & communication | 2014 |
| IT Xtreme Limited | Extraterritorial | 2003 |
| Italian Terracotta Company Limited | Wholesale & retail | 2002 |
| ITS Consultancy Services Ltd | Administrative & support | 2009 |
| Ivan's Village Foods Ltd | Hospitality | 2023 |
| J & D Construction Limited | Construction | 2016 |
| J & J Accounting Services Ltd | Professional & scientific | 2010 |
| J & R Car and Van Hire Limited | Administrative & support | 2011 |
| J Castle Electrical Ltd | Construction | 2025 |
| J Crawley Commercial Consultant Ltd | Professional & scientific | 2024 |
| J Horwood Plumbing Limited | Construction | 2008 |
| J P J C Limited | Real estate | 2013 |
| J Ruby Ltd | Real estate | 2015 |
| J&K Construction Services Ltd | Construction | 2022 |
| J&R Self Storage Ltd | Other services | 2012 |
| J-Curve Ltd | Professional & scientific | 2025 |
| J.C. Dudley & Co. Ltd | Wholesale & retail | 1983 |
| J.C. Dudley Holdings Ltd | Financial services | 2008 |
| J.J. Engineers Supplies Limited | Wholesale & retail | 1999 |
| J.T.W. Builders LLP | | 2016 |
| J1FIRE Ltd | Professional & scientific | 2023 |
| J4 Cleaning Services Limited | Administrative & support | 2016 |
| J4 Homes Limited | Real estate | 2019 |
| J4 Supported Living Services Ltd | Health & social care | 2025 |
| Jacktone Limited | Real estate | 2003 |
| Jakes Ginale Ltd | Other services | 2017 |
| Jakes Holdings Limited | Wholesale & retail | 2020 |
| James Haydon Limited | Financial services | 1961 |
| James Waite Estates Ltd | Real estate | 2023 |
| Jamie Pound Dog Training Limited | Other services | 2019 |
| Jamieson Berkeley Properties Limited | Real estate | 2012 |
| JAN Harrison Maternity Ltd | Health & social care | 2020 |
| Jane Duncan Properties Limited | Construction | 2003 |
| Janno Productions Limited | Information & communication | 2015 |
| Jared James Associates Limited | Administrative & support | 1995 |
| JAS & PLA Thia Kitchen Limited | Hospitality | 2024 |
| JAX Consultants Limited | Professional & scientific | 2023 |
| JAY Thomson Ltd | Information & communication | 2024 |
| JB Equipment Ltd | Manufacturing | 2019 |
| JCS Building Supplies Ltd | Wholesale & retail | 2026 |
| JD Motorworks Ltd | Wholesale & retail | 2021 |
| Jdallow & Co Ltd | Construction | 2024 |
| Jears Holdings Limited | Real estate | 2020 |
| JEM Security (Holdings) Limited | Financial services | 2024 |
| Jennifer Wilson Associates Limited | Professional & scientific | 2020 |
| Jenny Cader Clinic & Training Ltd | Other services | 2015 |
| JG Resin Ltd | Manufacturing | 2023 |
| JH Business Wise Limited | Administrative & support | 2004 |
| JH Fencing Limited | Construction | 2005 |
| JHK Holdings Ltd | Financial services | 2020 |
| JHO Accounts and Taxation Service Ltd | Professional & scientific | 2024 |
| Jinca Limited | Information & communication | 2005 |
| JJH Property Renovations Ltd | Real estate | 2026 |
| JJP Training Ltd | Arts & recreation | 2014 |
| Jjsk Enterprises Ltd | Transport & logistics | 2007 |
| JM Project Management Limited | Professional & scientific | 2012 |
| JMC 2025 Ltd | Wholesale & retail | 2025 |
| JMC Health Ltd | Health & social care | 2018 |
| JMF Plant Hire Limited | Administrative & support | 2016 |
| JMR Brickwork Limited | Construction | 2019 |
| JOG on Berkhamsted LLP | | 2017 |
| John COX & SON Motor Engineers Ltd | Wholesale & retail | 2007 |
| John Green (Building Contractors) Limited | Real estate | 1987 |
| John Madge Limited | Construction | 1962 |
| John Nash & Co (Amersham) Limited | Real estate | 2020 |
| Johnny Dufort Photography Ltd | Administrative & support | 2017 |
| Jojiuk Limited | Hospitality | 2026 |
| Jolly Unicorn Limited | Hospitality | 2018 |