| Ideas by Lunas Limited | Wholesale & retail | 2018 |
| Idec Ltd | Construction | 2007 |
| Identity & Access Solutions Ltd | Information & communication | 2024 |
| Identity Therapeutic Services Limited | Health & social care | 2021 |
| Idesign Services Ltd | Professional & scientific | 2020 |
| IDI Security Ltd | Administrative & support | 2025 |
| Idiculla Limited | Information & communication | 2016 |
| Idiots Anonymous Movie Limited | Information & communication | 2024 |
| Idoceo Labs Limited | Information & communication | 2013 |
| Idoceo Studios Ltd | Information & communication | 2020 |
| Idos London Ltd | Construction | 2025 |
| Idoz Group Ltd | Information & communication | 2019 |
| Idrop Limited | Information & communication | 2004 |
| IDS Connect Ltd | Information & communication | 2020 |
| IDS Media UK Limited | Information & communication | 1991 |
| IDW Engineering Limited | Professional & scientific | 2019 |
| IE Investment Limited | Construction | 2025 |
| IEE Consultancy Limited | Professional & scientific | 2018 |
| IES Data Cable Test Limited | Manufacturing | 2019 |
| IF Events Limited | Other services | 2023 |
| IF Finishes Ltd | Construction | 2020 |
| Ifeoluwa Mission (Chrislam) | Extraterritorial | 2010 |
| Ifeshow Limited | Wholesale & retail | 2026 |
| Ifit-Homes Limited | Construction | 2015 |
| Iforg Limited | Information & communication | 2002 |
| IG Engineering & Systems Limited | Professional & scientific | 2026 |
| IGA Signalling Limited | Construction | 2011 |
| Igli Ltd | Health & social care | 2017 |
| Igli Property Management Ltd | Real estate | 2026 |
| Igloo Renewable Assets Limited | Administrative & support | 2020 |
| Igloodomehire Ltd | Administrative & support | 2025 |
| Ignas Logistic Ltd | Transport & logistics | 2019 |
| Ignite (Acorns) Limited | Financial services | 2024 |
| Igrowcareers Ltd | Administrative & support | 2020 |
| IGS 1 Southampton Welding Ltd | Construction | 2018 |
| Igsp Consulting Limited | Financial services | 2018 |
| IH Window Cleaning Ltd | Administrative & support | 2018 |
| Ihca Limited | Professional & scientific | 2011 |
| IHD Architectural Services Ltd | Professional & scientific | 2008 |
| Ihome Furniture and Furnishing Ltd | Wholesale & retail | 2021 |
| IHS & NAS Ltd | Arts & recreation | 2026 |
| IHS Braxell Limited | Real estate | 2019 |
| Ihsumra Limited | Arts & recreation | 2016 |
| Iideel Ltd | Extraterritorial | 2022 |
| Iivari Limited | Financial services | 2020 |
| Ijequal Limited | Transport & logistics | 2013 |
| Ikidz Training and Consultancy Ltd | Administrative & support | 2010 |
| Ikoa Limited | Transport & logistics | 2019 |
| Ikon Company Services Limited | Administrative & support | 2016 |
| IL Fratelli Ltd | Hospitality | 2022 |
| ILA Consulting Limited | Professional & scientific | 2018 |
| Iles Property Limited | Real estate | 2006 |
| Ilex Homecare Ltd | Health & social care | 2025 |
| Ilgeth Design Ltd | Wholesale & retail | 2013 |
| Ilia Enteprise Ltd | Wholesale & retail | 2023 |
| Ilikegoingout.Com Ltd | Real estate | 2015 |
| Ilite Ledlighting Ltd | Manufacturing | 2022 |
| Illes Popovics Ltd | Transport & logistics | 2019 |
| Illuminated Canvas Holding Company Limited | Manufacturing | 2014 |
| Illyria Marine Consultancy Ltd | Professional & scientific | 2014 |
| Illyrianbiba Ltd | Transport & logistics | 2025 |
| ILM Kitchens & Bathrooms Ltd | Construction | 2014 |
| Ilocram Assets Management Ltd | Administrative & support | 2010 |
| Ilocram Ukeig | | 2011 |
| Ilterler Ltd | Wholesale & retail | 2021 |
| Ilym Ventures Ltd | Information & communication | 2021 |
| IM Facade Limited | Construction | 2016 |
| Im-Press Promotions Southampton Limited | Administrative & support | 2003 |
| IMA Consultancy Limited | Information & communication | 2009 |
| Image Insight Ltd | Wholesale & retail | 2014 |
| Image Perception Ltd | Manufacturing | 2016 |
| Images at Photo Solutions Limited | Other services | 2006 |
| Images Hair and Beauty Ltd | Other services | 2018 |
| Imaginarium Books Limited | Wholesale & retail | 2022 |
| Imagine Electrical Ltd | Construction | 2024 |
| Imagine Home Improvements Ltd | Construction | 2018 |
| IME International Ltd | Real estate | 2025 |
| Imed Contract Services Limited | Construction | 2020 |
| Imeta Holdings Ltd | Information & communication | 2012 |
| Imeta Technologies Limited | Information & communication | 2000 |
| Imetis Limited | Information & communication | 2012 |
| IMG Consultants Ltd | Information & communication | 2011 |
| Imgvue Ltd | Information & communication | 2015 |
| Imicast Ltd. | Information & communication | 2012 |
| Imlandris Investments Limited | Real estate | 2018 |
| Imlt Limited | Health & social care | 2024 |
| IMM (Hampshire) Ltd | Financial services | 2002 |
| IMM Enterprises Limited | Wholesale & retail | 2022 |
| IMM Services Limited | Wholesale & retail | 1999 |
| Immerse House Ltd | Manufacturing | 2023 |
| Imorphr Ltd. | Information & communication | 2019 |
| Imove (South) Ltd | Real estate | 2015 |
| Impact Building Projects Ltd | Construction | 2024 |
| Impact Electrical Ltd. | Administrative & support | 2015 |
| Impact Festival Ltd | Wholesale & retail | 2019 |
| Impala Butchery and Grill Ltd | Wholesale & retail | 2026 |
| Impala Family Butchers Ltd | Wholesale & retail | 2019 |
| Impartial Financial Solutions LLP | | 2007 |
| Impartial Mortgage & Protection Ltd | Financial services | 2015 |
| Impasse Fire Door Services Ltd | Construction | 2021 |