| World Media Group Ltd | Information & communication | 2023 |
| Worldwide Wool Felts Limited | Manufacturing | 1990 |
| Worm London Limited | Wholesale & retail | 2018 |
| Wrap Mode Limited | Wholesale & retail | 2024 |
| Wren Psychology Ltd | Health & social care | 2021 |
| Wshack Ltd | Information & communication | 2024 |
| Wutzler Creative Limited | Information & communication | 2023 |
| Wyming Brook Consulting Ltd | Professional & scientific | 2024 |
| X-Land Properties Limited | Professional & scientific | 2004 |
| Xemption Limited | Administrative & support | 2021 |
| Xlabs Global Ltd | Information & communication | 2014 |
| Xlsr Estates Limited | Real estate | 2023 |
| Xlsr Group Ltd | Real estate | 2022 |
| XO Editorial Ltd | Information & communication | 2022 |
| XR Theatre Ltd | Arts & recreation | 2022 |
| Y Mohsen Ltd | Health & social care | 2023 |
| Yatton Investments Ltd | Households | 2026 |
| Yellow Trumpet Hotels Limited | Hospitality | 2024 |
| Yiral Limited | Construction | 2019 |
| Yoga Paradise Publications Limited | Other services | 2016 |
| Yotta Limited | Information & communication | 1986 |
| Youell Court Care Limited | Health & social care | 2025 |
| Young Folk Limited | Information & communication | 2015 |
| Young Giants Ltd | Education | 2020 |
| Your Social Insights Limited | Information & communication | 2015 |
| YUM & Dolce Ltd | Hospitality | 2002 |
| Zano Controls Limited | Wholesale & retail | 2010 |
| Zano Technology Limited | Manufacturing | 2026 |
| Zapallar Consulting Ltd | Professional & scientific | 2018 |
| Zare Ltd | Other services | 2023 |
| Zelamal Limited | Other services | 2011 |
| Zenith Noir Ltd | Real estate | 2010 |
| Zerberus Rapidus CIC | Education | 2025 |
| ZF Homes Ltd | Real estate | 2026 |
| Zion Care (ST Albans) Limited | Health & social care | 2008 |
| Zion Care Homes Limited | Health & social care | 2005 |
| Zion Care Limited | Health & social care | 2005 |
| Zion UK Properties Ltd | Households | 2023 |
| Zotti Consulting Ltd | Manufacturing | 2024 |
| Zytec Training Limited | Information & communication | 1996 |