| Islay Estates Company | Agriculture & fishing | 1928 |
| Islay Estates Company (Pier Project) Limited | Financial services | 2023 |
| Issec Limited | Agriculture & fishing | 2002 |
| Istek Support Ltd | Administrative & support | 2014 |
| Istek UK Limited | Information & communication | 1999 |
| Italiaverde Limited | Real estate | 2016 |
| ITC Technology Ltd | Information & communication | 2025 |
| Itonus Limited | Information & communication | 2012 |
| Itsalltechniq Ltd | Professional & scientific | 2022 |
| Itsm Associates Ltd | Information & communication | 2013 |
| Iunite Media Ltd | Manufacturing | 2021 |
| IV Winds Ltd | Information & communication | 2012 |
| Ivdp Ltd | Professional & scientific | 2023 |
| Iverna Trading Ltd | Wholesale & retail | 2018 |
| Ivester Court Maintenance Co. (1991) Limited | Households | 1991 |
| Ivor Perry Limited | Arts & recreation | 2000 |
| IVY Rose Jewellery Ltd | Other services | 2018 |
| Ivyblue Ltd | Administrative & support | 2010 |
| Ivydene Services Ltd | Health & social care | 2026 |
| Ivysound Limited | Professional & scientific | 2005 |
| IX Next GEN Ltd | Manufacturing | 2024 |
| J & K Care Specialists Limited | Health & social care | 2001 |
| J & K Dean Limited | Real estate | 2021 |
| J & R Hooper Farms Limited | Agriculture & fishing | 1954 |
| J a Mackenzie Limited | Transport & logistics | 2012 |
| J Amor Services Limited | Wholesale & retail | 2017 |
| J Brockway Solutions Ltd | Construction | 2026 |
| J C B Garden Landscape Limited | Administrative & support | 2002 |
| J C F P Secretaries Ltd | Administrative & support | 2016 |
| J C T Developments Ltd | Administrative & support | 2011 |
| J Curnick & SON Ltd | Agriculture & fishing | 2005 |
| J D W Plumbing & Heating Services Ltd | Other services | 2014 |
| J Drewitt & Sons Limited | Construction | 2014 |
| J E C Reed Limited | Professional & scientific | 2011 |
| J G Engineering (Salisbury) Ltd | Professional & scientific | 2019 |
| J H Beckly & Co | | 1983 |
| J J & S Transport Limited | Transport & logistics | 1997 |
| J J M (2008) Limited | Extraterritorial | 2009 |
| J L Frampton & Sons (Spetisbury) Limited | Agriculture & fishing | 1959 |
| J M W Cars Limited | Wholesale & retail | 2016 |
| J Mann Associates Ltd | Administrative & support | 2003 |
| J Matthiae & Co Limited | Professional & scientific | 2010 |
| J O Thomas Limited | Professional & scientific | 2017 |
| J P Trustees Limited | Professional & scientific | 2008 |
| J Pike Aggregates Ltd | Transport & logistics | 2015 |
| J R Bodman Limited | Agriculture & fishing | 2005 |
| J R Hassan Property Ltd | Real estate | 2024 |
| J Smith Properties Ltd | Real estate | 2024 |
| J W Vines Limited | Construction | 2004 |
| J Waters Property Group Ltd | Real estate | 2025 |
| J&E Waterman Limited | Professional & scientific | 2012 |
| J&H Transport Solutions Ltd | Transport & logistics | 2021 |
| J&T Weeks Plumbing & Heating Limited | Construction | 2014 |
| J. a. Cooke Building Services Limited | Wholesale & retail | 2002 |
| J. C. G Integrity & Testing Ltd. | Extraterritorial | 2016 |
| J. F. Plumbing & Heating Ltd. | Construction | 2006 |
| J.A.G South Limited | Construction | 2025 |
| J.C. Dean (Haulage) Limited | Transport & logistics | 1972 |
| J.C.Carpets & Beds Limited | Wholesale & retail | 2013 |
| J.G. Chap Ltd | Construction | 2014 |
| J.J. Acquisitions Limited | Construction | 2006 |
| J.K. Brock Builders (Dereham) Limited | Construction | 1972 |
| J.L.Wardle Plastering Contractors Ltd | Construction | 2010 |
| J.M Varomua Ltd | Health & social care | 2023 |
| J.N.L Ltd | Construction | 2023 |
| J.R.Williams(Chandlery)Limited | Real estate | 1950 |
| J.S. Thomas Contractors Limited | Construction | 2001 |
| J4 Management Limited | Households | 2005 |
| Jack Ryan Transport Ltd | Transport & logistics | 2019 |
| Jack Whitehart Ltd | Information & communication | 2011 |
| Jackson Builders (South) Ltd | Construction | 2006 |
| Jackson Cook Limited | Professional & scientific | 2018 |
| Jacob Boston Fine Art Limited | Wholesale & retail | 2022 |
| Jacobs Holdings Salisbury Ltd | Financial services | 2023 |
| Jacqueline Webb & Co. Ltd. | Information & communication | 2007 |
| Jacques Noel Industries Limited | Information & communication | 2015 |
| Jacquis Sunbed Studio Ltd | Other services | 2023 |
| Jade Scaffolding Limited | Construction | 2004 |
| Jadtec Ltd | Extraterritorial | 2019 |
| Jaguar Executive Taxi Ltd | Transport & logistics | 2020 |
| Jah's Will Limited | Health & social care | 2020 |
| Jaiteh Shipping and Logistics Ltd | Transport & logistics | 2016 |
| Jake Eastham Photographer Ltd | Professional & scientific | 2018 |
| Jamalu Limited | Professional & scientific | 2009 |
| Jamatelier Ltd | Wholesale & retail | 2025 |
| Jamelle Limited | Real estate | 2026 |
| James Allied Engineering Limited | Administrative & support | 2004 |
| James Baker Holdings Limited | Financial services | 2026 |
| James Benedict Ltd | Other services | 2012 |
| James Bros Property Services Limited | Real estate | 2018 |
| James Burton Construction & Management Ltd | Construction | 2014 |
| James Burton Joinery Limited | Manufacturing | 2023 |
| James Burton Properties Limited | Real estate | 2024 |
| James Court RTM Company Limited | Households | 2014 |
| James Francis Touring Ltd | Information & communication | 2026 |
| James HAY Administration Company Limited | Financial services | 2000 |
| James HAY Holdings Limited | Financial services | 1990 |
| James HAY Partnership Limited | Professional & scientific | 2016 |
| James HAY Pension Trustees Limited | Financial services | 1979 |
| James HAY Wrap Managers Limited | Financial services | 2003 |