| Incoming Thought Limited | Information & communication | 2006 |
| Independent Fibre Retail Limited | Information & communication | 2010 |
| Independent Social Work Experts Limited | Health & social care | 2018 |
| Indian Spice (Isleworth) Ltd | Hospitality | 2024 |
| Indoor Outdor Ltd | Wholesale & retail | 2021 |
| Ineffable Interiors Limited | Professional & scientific | 2020 |
| Infinity Extensions Limited | Construction | 2018 |
| Infinity Yoga Clothing Limited | Wholesale & retail | 2016 |
| Infoedge UK PVT Ltd | Wholesale & retail | 2024 |
| Ingletone Estate Limited | Real estate | 2021 |
| INK Property Ltd | Real estate | 2023 |
| Inoubliable Ltd | Real estate | 2015 |
| Inovi Group Ltd | Information & communication | 2026 |
| Inrules Ltd | Information & communication | 2013 |
| Insignia Global Limited | Construction | 2018 |
| Inspiration Saloon Ltd | Other services | 2026 |
| Inspire Hounslow | Health & social care | 1998 |
| Instrumentation Testing Solutions Ltd | Professional & scientific | 2026 |
| Intactilis Limited | Information & communication | 2024 |
| INTEGR8MPS Limited | Administrative & support | 2025 |
| Integra Law Recruitment Limited | Administrative & support | 2026 |
| Integral Security Xssurance Limited | Administrative & support | 2013 |
| Intelligent Business Management Limited | Other services | 2013 |
| Intellisense Programming Ltd | Information & communication | 2010 |
| Intellisense Real Estate Company Ltd | Real estate | 2024 |
| Interlanguage Limited | Education | 2006 |
| Intermediary London Ltd | Professional & scientific | 2011 |
| International Channel Pack Distribution Limited | Information & communication | 2015 |
| International Precious Metals Limited | Wholesale & retail | 2014 |
| Interventional Radiology London Ltd | Health & social care | 2014 |
| Invent+ Ltd | Construction | 2014 |
| Inventive Designs London Ltd | Construction | 2014 |
| Invest and Manage Properties Limited | Real estate | 2018 |
| Invest Estates Investment Ltd | Financial services | 2019 |
| Invest Estates UK Ltd | Wholesale & retail | 2017 |
| Investwise International Limited | Financial services | 2016 |
| Iowemusic Production Ltd | Information & communication | 2021 |
| IP Fire & Security Limited | Construction | 2009 |
| Ipanema Travel Limited | Administrative & support | 2005 |
| IQ Renovation Ltd | Construction | 2019 |
| Iraj Management Solutions Limited | Professional & scientific | 2014 |
| Irongate Point Limited | Real estate | 2003 |
| Ironoak Limited | Construction | 2026 |
| IRR International Limited | Health & social care | 2022 |
| IRT Electrical Services Limited | Construction | 2025 |
| Iryna's Cleaning Limited | Administrative & support | 2014 |
| ISD Contracting Limited | Information & communication | 2007 |
| Isleworth & Hounslow Charity Limited | Hospitality | 2005 |
| Isleworth and Syon School for Boys | Education | 2012 |
| Isleworth Angling & Tackle Ltd | Wholesale & retail | 2019 |
| Isleworth Bakery and Traditional Ltd | Manufacturing | 2026 |
| Isleworth Bakery Ltd | Wholesale & retail | 2025 |
| Isleworth Bathrooms Ltd | Wholesale & retail | 2022 |
| Isleworth Building Contractors Ltd | Construction | 2023 |
| Isleworth Building Ltd | Construction | 2025 |
| Isleworth Car Wash Ltd | Other services | 2017 |
| Isleworth Deen Centre | Health & social care | 2011 |
| Isleworth Food & Wine Ltd | Wholesale & retail | 2014 |
| Isleworth Greengrocer Limited | Wholesale & retail | 2019 |
| Isleworth LLP | | 2016 |
| Isleworth Service Centre Limited | Wholesale & retail | 2013 |
| Isleworth Tyres Ltd | Wholesale & retail | 2016 |
| Istead Consulting Ltd | Professional & scientific | 2025 |
| Istudyuk Ltd | Education | 2017 |
| IT Help Line Ltd | Information & communication | 2020 |
| Italiano Pizza Ltd | Hospitality | 2021 |
| Iunfold Ltd | Information & communication | 2022 |
| Ivoryglass Productions Ltd | Manufacturing | 2025 |
| IVS Group Limited | Wholesale & retail | 1998 |
| IVS Limited | Real estate | 2003 |
| IVS Mobile Ltd | Wholesale & retail | 2006 |
| Ivybridgelink | Hospitality | 2000 |
| Ivyease Technologies Ltd | Wholesale & retail | 2026 |
| J Hamlin Consulting Limited | Professional & scientific | 2023 |
| J Loyal Property Limited | Real estate | 2025 |
| J&H Food and Wine Limited | Wholesale & retail | 2026 |
| J&H Vyas Properties Ltd | Real estate | 2020 |
| J&S Construction Builds Ltd | Construction | 2024 |
| J1GSAW Ltd | Construction | 2018 |
| Jabax Ltd | Transport & logistics | 2020 |
| Jack Farrow Limited | Information & communication | 2014 |
| Jacket Hunter Ltd | Wholesale & retail | 2024 |
| Jacnet Investments Limited | Construction | 2020 |
| Jacobs and Co Logistics Ltd | Transport & logistics | 2018 |
| Jade Labour Services Limited | Construction | 2018 |
| Jadida Construction Ltd | Construction | 2026 |
| Jafar Property Ltd | Households | 2023 |
| Jagdev Peak Performance Ltd | Education | 2025 |
| Jaggi & Jaggi Ltd | Real estate | 2015 |
| Jambo 1 Ltd | Transport & logistics | 2025 |
| James Breward Limited | Arts & recreation | 2010 |
| James Electrical Services Ltd | Construction | 2023 |
| James Griffin Design Ltd | Professional & scientific | 2016 |
| James Plumbing and Heating Limited | Construction | 2024 |
| Jamjar Creative Services Ltd | Information & communication | 2014 |
| JAN Catering Ltd | Hospitality | 2025 |
| JAN Construction Ltd | Construction | 2021 |
| Janbal Limited | Wholesale & retail | 2024 |
| Jane Macharia Limited | Health & social care | 2018 |
| JAP Performance Holdings Limited | Administrative & support | 2012 |