| Iterxus Ltd | Professional & scientific | 2025 |
| Itnerary Ltd | Professional & scientific | 2018 |
| ITPRO306.CO.UK Limited | Information & communication | 2018 |
| ITS Products Limited | Manufacturing | 2015 |
| Itsol Limited | Information & communication | 2014 |
| Itsrodells Limited | Hospitality | 2011 |
| ITY Ltd | Other services | 2024 |
| Iv-Offsite Designs Limited | Professional & scientific | 2015 |
| IVA Tech Limited | Information & communication | 2015 |
| Ivangor Contractor Ltd | Construction | 2025 |
| Ivco Holding Limited | Financial services | 2025 |
| IVM Service Ltd | Construction | 2018 |
| Ivory Bloom Ltd | Wholesale & retail | 2025 |
| IVU Electrical Ltd | Construction | 2020 |
| IVY ROW Ltd | Professional & scientific | 2025 |
| IVY Services London Ltd | Arts & recreation | 2022 |
| IWK Watford Ltd | Hospitality | 2023 |
| Iworklife Limited | Administrative & support | 2006 |
| Ixion Creations Limited | Information & communication | 2014 |
| IY Diagnostics and Recovery Solutions Ltd | Other services | 2020 |
| IZ Group Construction Ltd | Construction | 2026 |
| Izincare Ltd | Health & social care | 2016 |
| Izsk Ltd | Real estate | 2020 |
| I’Min Studio Ltd | Arts & recreation | 2026 |
| J & G Developments UK Limited | Construction | 2008 |
| J & L Research Ltd | Financial services | 2012 |
| J & T Electrical Distribution Limited | Wholesale & retail | 2016 |
| J a FOX Ltd | Agriculture & fishing | 2017 |
| J a Johnson Limited | Professional & scientific | 2022 |
| J a K Jewellers Limited | Transport & logistics | 2007 |
| J a Property Rentals Ltd | Real estate | 2024 |
| J a Quantum Leap Ltd | Hospitality | 2017 |
| J and J Property Limited | Administrative & support | 2008 |
| J B Floortech Limited | Other services | 1995 |
| J B Mechanical Contractors Ltd | Construction | 2016 |
| J Barton Solutions Ltd | Information & communication | 2010 |
| J Brogan Brickwork Limited | Construction | 2007 |
| J C Harrow Limited | Construction | 2021 |
| J Catchpole & Co Ltd | Professional & scientific | 2018 |
| J Clarke Consulting Ltd | Professional & scientific | 2023 |
| J Class Enterprises Ltd | Professional & scientific | 2023 |
| J Corlis Productions Ltd | Information & communication | 2025 |
| J D Wetherspoon PLC | Hospitality | 1983 |
| J D Wetherspoon Property Holdings Ltd | Hospitality | 2011 |
| J Forrest Ltd | Health & social care | 2022 |
| J Foulston Consulting Ltd | Administrative & support | 2016 |
| J Gibbs Building Services Ltd | Construction | 2023 |
| J Gilmartin Ltd | Real estate | 2021 |
| J L Frost & SON Wind Farm Limited | Energy | 2015 |
| J M Dhindsa Ltd | Real estate | 2021 |
| J M Driveway and Patios Ltd | Administrative & support | 2025 |
| J M Fussey Productions Limited | Information & communication | 2011 |
| J Madge Carpentry Ltd | Construction | 2022 |
| J Manfredini Ltd | Financial services | 2019 |
| J N D Motors Ltd | Wholesale & retail | 2017 |
| J Nevin Limited | Construction | 2017 |
| J Noone Consultancy Limited | Professional & scientific | 2010 |
| J P 2 Limited | Real estate | 2009 |
| J P Salomon & Co. Limited | Professional & scientific | 2003 |
| J Patel Dent Ltd | Health & social care | 2025 |
| J Pellow & SON Limited | Construction | 2007 |
| J R Findlay Ltd | Extraterritorial | 2022 |
| J R M Dhindsa Limited | Real estate | 2019 |
| J Ramms Ltd | Information & communication | 2020 |
| J Rixon Carpentry Ltd | Construction | 2019 |
| J Russell Management Services Limited | Financial services | 2008 |
| J Scholtz Consultancy Ltd | Professional & scientific | 2014 |
| J Sommer Ltd | Financial services | 2021 |
| J Squared Global Limited | Wholesale & retail | 2025 |
| J Stores Management Services Limited | Real estate | 2024 |
| J Stratton Ltd | Other services | 2017 |
| J W Car Agency Limited | Wholesale & retail | 2008 |
| J&A Health Solutions Ltd | Professional & scientific | 2019 |
| J&A Venture Group Ltd | Financial services | 2025 |
| J&E Projects Limited | Wholesale & retail | 2004 |
| J&H Top Construction Ltd | Construction | 2025 |
| J&J Construction Consultants Ltd | Construction | 2015 |
| J&J Enterprises Ltd | Wholesale & retail | 2026 |
| J&K Data Solutions Ltd | Information & communication | 2016 |
| J&Kt Property Ltd | Real estate | 2026 |
| J&M Gallagher Builders (Holdings) Limited | Financial services | 2019 |
| J&M IT Services Ltd | Information & communication | 2010 |
| J&N Ever Fresh Market Limited | Wholesale & retail | 2025 |
| J&Pw Developments Ltd | Construction | 2018 |
| J&S UK Properties Ltd | Real estate | 2023 |
| J'Écoute Limited | Administrative & support | 2026 |
| J. Kendal GAS, Plumbing, and Heating Ltd | Construction | 2019 |
| J. Mcgowan & Sons Ltd | Construction | 2018 |
| J.& M.Gallagher(Builders)Limited | Real estate | 1961 |
| J.E. Industries Ltd | Real estate | 2026 |
| J.F. Kempster & Sons Limited | | 1976 |
| J.Flynn Limited | Construction | 1997 |
| J.Jar Vehicle Services Ltd | Wholesale & retail | 2022 |
| J.Peters Agricultural Services Ltd | Agriculture & fishing | 2024 |
| J.R.A Property Services Ltd | Construction | 2023 |
| J.T. Sets Limited | Construction | 2009 |
| J2Z Ltd | Wholesale & retail | 2026 |
| JA Health (Chiropractic) Limited | Health & social care | 2014 |
| JAA Wealth Limited | Real estate | 2019 |
| JAB Technologies Ltd | Information & communication | 2012 |