| Integrated Dermatology Solutions Limited | Health & social care | 2015 |
| Integrated Digital Security Limited | Administrative & support | 2007 |
| Intelligent Buying Limited | Professional & scientific | 2011 |
| Intelligent Learning Limited | Education | 2018 |
| Inter City Robotics Limited | Construction | 2012 |
| Interior Ceramics Limited | Construction | 2018 |
| International Printer Parts Ltd | Wholesale & retail | 2024 |
| International Seal Co. Ltd | Wholesale & retail | 2026 |
| Intertherm Insulation Services Ltd | Construction | 2014 |
| Into the Garden Room Ltd | Construction | 2015 |
| Investigate 2 Educate CIC | Education | 2025 |
| Investment Property Management Ltd | Real estate | 2013 |
| Investments and Business Administration Limited | Professional & scientific | 2021 |
| Invictus Cleaning Services Ltd | Administrative & support | 2024 |
| ION Consultancy Ltd | Real estate | 2023 |
| IP Real Estate Limited | Real estate | 2022 |
| IQ London Limited | Wholesale & retail | 2024 |
| IQA Partners Limited | Professional & scientific | 2024 |
| Iqonic Aesthetics Ltd | Administrative & support | 2020 |
| IR35 Limited | Professional & scientific | 1999 |
| Ireland Property Holdings Ltd | Real estate | 2021 |
| Ironbuilt Gym Ltd | Other services | 2025 |
| Isaac Clarke and Associates Limited | Arts & recreation | 2010 |
| Iscreenyouscreen.Com Ltd. | Administrative & support | 2009 |
| Ishmail & Associates Ltd | Health & social care | 2020 |
| Ismart Designs Limited | Professional & scientific | 2017 |
| ISO Management Consultants Limited | Professional & scientific | 2020 |
| IT People Recruitment Ltd | Administrative & support | 2024 |
| Iterum Solutions Limited | Information & communication | 2003 |
| Itoli Limited | Information & communication | 2007 |
| Itsm Matters Limited | Information & communication | 2016 |
| IVY Marketing Properties (Essex) Ltd | Real estate | 2020 |
| IVY Marketing Services Ltd | Administrative & support | 2017 |
| J & C Tanning Studios Ltd | Other services | 2002 |
| J & CJ Frozen Foods Limited | Wholesale & retail | 2021 |
| J & F Cleaning & Maintenance Ltd | Administrative & support | 2012 |
| J & K O'Brien Limited | Financial services | 2015 |
| J & S Studio Property Services Ltd | Real estate | 2022 |
| J B Transport & Couriers Ltd | Transport & logistics | 2008 |
| J Blakemore Consulting Ltd | Professional & scientific | 2022 |
| J Bloor Oak Limited | Construction | 2016 |
| J Bloor Plant Limited | Administrative & support | 2021 |
| J Caesar Limited | Health & social care | 2025 |
| J Carroll Engineering Services Limited | Professional & scientific | 2023 |
| J D Contracts Limited | Construction | 2015 |
| J D Plumbing & Tiling Limited | Administrative & support | 2005 |
| J Dear Ltd | Wholesale & retail | 2021 |
| J F House Ltd | Construction | 2026 |
| J J Leisure & Social Limited | | 1989 |
| J Jadhav Associates Limited | Health & social care | 2012 |
| J L Murphy Limited | Construction | 2006 |
| J Lindfield Electrical Limited | Construction | 2017 |
| J Lynch and SON Limited | Construction | 2024 |
| J M Formwork Ltd | Construction | 2010 |
| J P & M D Properties Ltd. | Construction | 2014 |
| J P Gatrell Limited | Construction | 1997 |
| J R Friend Ltd | Professional & scientific | 2026 |
| J Speck Plumbing and Heating Ltd | Construction | 2021 |
| J T S T Property Consultants Ltd | Professional & scientific | 2014 |
| J&E Removals and Clearances Ltd. | Other services | 2020 |
| J&J Watts Holdings Ltd | Financial services | 2025 |
| J&L Electrical Contractors Ltd | Construction | 2021 |
| J&S Toilet Hire Ltd | Administrative & support | 2024 |
| J. Bloor Construction Limited | Construction | 2015 |
| J. Close Developments Limited | Construction | 2017 |
| J. Landy & Co Shopfitting Services Limited | Construction | 2015 |
| J.A.C Groundwork & Civil Engineering Ltd | Construction | 2015 |
| J.M.Evenett Limited | Construction | 2019 |
| J.S. Wines & Spirits Limited | Transport & logistics | 1991 |
| JA Traders Ltd | Other services | 2017 |
| Jabor Enterprises Limited | Financial services | 2017 |
| JAC Road Haulage Ltd | Construction | 2017 |
| Jack Gundry Ltd | Real estate | 2023 |
| Jack Parr Limited | Arts & recreation | 2019 |
| Jack Stone Staircases Ltd | Construction | 2020 |
| Jackson Frye Ltd | Construction | 2014 |
| Jade Coffey Ltd | Health & social care | 2025 |
| Jaec Properties Limited | Real estate | 2022 |
| JAG Building and Property Services Ltd | Construction | 2023 |
| Jago Corporate Finance Limited | Financial services | 2009 |
| Jairus Anaesthetic Services Ltd | Health & social care | 2011 |
| JAJ Housing Limited | Real estate | 2023 |
| JAK Software Consulting Ltd | Information & communication | 2022 |
| JAM Software Limited | Information & communication | 2015 |
| Jambea Limited | Financial services | 1977 |
| James Achille Blue Q Mortgage Limited | Financial services | 2014 |
| James Alexander Estates Limited | Real estate | 2015 |
| James Bull & Associates Limited | Professional & scientific | 2011 |
| James Bull & Counter Limited | Professional & scientific | 2006 |
| James LEE Photography Limited | Professional & scientific | 2021 |
| James Moseley Properties Limited | Real estate | 2015 |
| James O'Brien Holdings Limited | Administrative & support | 2003 |
| James Stephens Jewellers Limited | Wholesale & retail | 2008 |
| Jarisco Property Limited | Real estate | 2021 |
| Jarvis & Co. Business Services Limited | Professional & scientific | 2003 |
| Jarvis Development Group Ltd | Construction | 2022 |
| Jasb Consulting Limited | Professional & scientific | 2017 |
| Jaspsa Ltd | Real estate | 2017 |
| Jate Electrical Ltd | Construction | 2024 |
| JAX Virtual Services Ltd | Administrative & support | 2020 |