| Industrial Software & Controls Limited | Professional & scientific | 2009 |
| Industrial Support Limited | Construction | 2017 |
| Infinity Path Ltd | Real estate | 2024 |
| Inflexium Limited | Professional & scientific | 2025 |
| Information Reports Limited | Information & communication | 2009 |
| Infrastructure 360 Ltd | Information & communication | 2026 |
| Infrastructure Design Limited | Administrative & support | 2000 |
| Infrastructure Managed Services Limited | Administrative & support | 2017 |
| Ingenuity Estates Limited | Real estate | 2022 |
| Ingram Court (Freehold) Limited | Households | 1998 |
| Ingsocdev Ltd | Information & communication | 2021 |
| Initium (Design Build Contract) Limited | Administrative & support | 2013 |
| INK Heaven Tattoos Ltd | Other services | 2021 |
| Inkerpole Place (Chelmsford) Management Company Limited | Households | 1987 |
| Innis Independent Consultancy Limited | Hospitality | 2008 |
| Innox Holdings Ltd | Financial services | 2026 |
| Inpo Limited | Wholesale & retail | 2021 |
| Inside Sourcing Ltd | Wholesale & retail | 2026 |
| Insight Relocations Limited | Hospitality | 2021 |
| Insomnia Music Management Limited | Arts & recreation | 2009 |
| Insomnia Music UK Ltd | Administrative & support | 2000 |
| Inspirae Ltd | Professional & scientific | 2025 |
| Inspire Labs Ltd | Information & communication | 2011 |
| Install & Maintain Electrical Limited | Construction | 2019 |
| Instant Equity Limited | Construction | 2006 |
| Instant Heating Solutions Ltd | Manufacturing | 2018 |
| Institute of the Motor Industry(The) | Professional & scientific | 1927 |
| Insup Limited | Construction | 2025 |
| Insure Once Limited | Financial services | 2013 |
| INT Electrical Ltd | Construction | 2023 |
| Integrated Brand Management Services Limited | Other services | 2020 |
| Integrative Health Consulting Ltd | Health & social care | 2003 |
| Integrityapplianceinstallation Ltd | Construction | 2023 |
| Interactive Mortgage Adviser Ltd | Financial services | 2024 |
| Interactive Mortgage Advisor Ltd | Financial services | 2024 |
| Intercake UK Limited | Wholesale & retail | 2012 |
| Interiord Ltd | Construction | 2018 |
| Interlinked Facilities Management Ltd | Professional & scientific | 2021 |
| Interlinked Fire & Security Ltd | Administrative & support | 2022 |
| Interlinked Group Ltd | Financial services | 2021 |
| Interlinked Ltd | Administrative & support | 2014 |
| International Broadcasting Convention LLP | | 2023 |
| International Centre for Transactional Analysis Qualifications CIC | Professional & scientific | 2020 |
| International Friends of the National Gallery of Ireland Limited | Education | 1996 |
| Intor Design Limited | Construction | 2006 |
| Invapay Ltd | Professional & scientific | 2023 |
| Invapay Payments Ltd | Professional & scientific | 2023 |
| Invest Savvy Limited | Professional & scientific | 2024 |
| Invictus Capital Ltd | Financial services | 2019 |
| Involve Investment Management Limited | Financial services | 2022 |
| Involve Service Solutions Limited | Professional & scientific | 2020 |
| Ioco Solutions Limited | Information & communication | 2008 |
| IPT Networks Ltd | Information & communication | 2009 |
| IPV6 Limited | Information & communication | 2008 |
| Iroko Homes Ltd | Real estate | 2023 |
| Irwin Partners Ltd | Professional & scientific | 2025 |
| Isabelle James Ltd | Wholesale & retail | 2024 |
| Isolveit Ltd | Information & communication | 2003 |
| Issi Limited | Other services | 2008 |
| Istec Services Limited | Professional & scientific | 1989 |
| IT Luggage Limited | Wholesale & retail | 1985 |
| IT Started With LU CIC | Health & social care | 2023 |
| ITS Digital Limited | Information & communication | 2007 |
| J & K Fleet Consultancy Limited | Professional & scientific | 2015 |
| J & M (2025) Limited | Administrative & support | 2025 |
| J & R Flowers Limited | Wholesale & retail | 2019 |
| J & R Heating Solutions Limited | Construction | 2021 |
| J & W Consultancy Limited | Administrative & support | 2011 |
| J B Chauffeurs Limited | Transport & logistics | 2008 |
| J C Straker Ltd | Manufacturing | 2016 |
| J Cano French Polishers and Joinery Ltd | Construction | 2013 |
| J Cook Landscapes Limited | Administrative & support | 2014 |
| J D Tree Care Limited | Administrative & support | 2018 |
| J F Cars (Herts) Limited | Wholesale & retail | 2016 |
| J H Electrical Installations Limited | Construction | 2019 |
| J H Fage & SON Limited | Construction | 2012 |
| J M Heating & Plumbing Ltd | Construction | 2018 |
| J R G S Heating Services Ltd | Construction | 2015 |
| J RAW Holdings Ltd | Real estate | 2018 |
| J W Fabrications Limited | Construction | 2012 |
| J W H Property Investments Limited | Real estate | 2018 |
| J W Hughes Property Holdings Ltd | Construction | 2021 |
| J W Hydraulics Limited | Manufacturing | 2011 |
| J&J Thomson Limited | Administrative & support | 2015 |
| J&S Electrical Installations Ltd | Construction | 2025 |
| J. B. Construction (East Anglia) Limited | Construction | 2002 |
| J. Ward Builders Limited | Construction | 2010 |
| J.I. Pallett Landscaping Limited | Construction | 2011 |
| J.S.M.H Services Ltd | Wholesale & retail | 2013 |
| J.W. Hughes Holdings Limited | Financial services | 2003 |
| Jack Dunning Ltd | Manufacturing | 2005 |
| Jackson Fletcher Limited | Construction | 2005 |
| Jadar Limited | Administrative & support | 1983 |
| Jaggers Academy Ltd | Arts & recreation | 2017 |
| Jaggers Productions Limited | Arts & recreation | 2019 |
| Jake Bingham Farriery Limited | Agriculture & fishing | 2026 |
| Jamarah Ltd | Real estate | 2014 |
| James Colli Signwriting Limited | Administrative & support | 2015 |
| James Douglas EOT Limited | Administrative & support | 2024 |
| James Douglas Limited | Manufacturing | 1995 |