| Abtap Limited | Construction | 2003 |
| Abul Media Ltd | Professional & scientific | 2024 |
| Abundantly Bliss Ltd | Professional & scientific | 2020 |
| Abventures Ltd | Real estate | 2024 |
| AC Financial Associates Limited | Administrative & support | 2013 |
| AC Three Ltd | Professional & scientific | 2016 |
| AC Training and Consulting Ltd | Professional & scientific | 2020 |
| ACA Support Services Limited | Administrative & support | 2019 |
| Acacia Lodge Freehold Company Limited | Real estate | 2011 |
| Acadomus Ltd | Administrative & support | 2021 |
| Acai Ltd | Financial services | 2013 |
| Acazam Ltd | Professional & scientific | 2022 |
| Acceleva Consulting Ltd | Professional & scientific | 2025 |
| Accelform Analytics & Optimisation Limited | Professional & scientific | 2011 |
| Access Labs Ltd | Professional & scientific | 2025 |
| Accessible Development Limited | Real estate | 2023 |
| Accident Specialists Watford Limited | Financial services | 2014 |
| Accountability Membership Club Ltd | Other services | 2025 |
| Accountability Solutions Limited | Financial services | 2009 |
| Accountancy Choice Limited | Professional & scientific | 2009 |
| Accountancy in Europe.Com Ltd | Professional & scientific | 2011 |
| Accountant YOU CAN Count on Ltd | Education | 2024 |
| Accountants for Good Ltd | Professional & scientific | 2022 |
| Accountax Business Solutions Ltd | Professional & scientific | 2005 |
| Accounting Space Ltd | Information & communication | 2020 |
| Accounting Sphere UK Ltd | Professional & scientific | 2012 |
| Accounts & Finance Limited | Professional & scientific | 2009 |
| Accounts by Balance Ltd | Professional & scientific | 2020 |
| Accounts for Barristers Ltd | Professional & scientific | 2021 |
| Accounts Tax Group Ltd | Professional & scientific | 2021 |
| Accountsassists Pro Limited | Information & communication | 2026 |
| Accrual & Unusual Ltd | Professional & scientific | 2025 |
| Accruetek Consulting Limited | Information & communication | 2012 |
| Accubalance Solutions Ltd | Professional & scientific | 2024 |
| Accucount Ltd | Extraterritorial | 2014 |
| Accuola Ltd | Professional & scientific | 2025 |
| Accurate Consultancy Limited | Information & communication | 2018 |
| Accurate Curtis Ltd | Construction | 2021 |
| Accurate Payroll and Bookkeeping Services Limited | Administrative & support | 2021 |
| Accurate Solutions Limited | Information & communication | 1990 |
| Accusafe Ltd | Wholesale & retail | 2019 |
| Accutech Consulting Limited | Information & communication | 2013 |
| Accuver Emea Ltd. | Wholesale & retail | 2004 |
| Accuwise Financial Solutions Limited | Professional & scientific | 2024 |
| Acdcat.Io Limited | Information & communication | 2019 |
| Acdi Electrovent Ltd | Construction | 2023 |
| Ace & Jack’S Poker League Ltd | Arts & recreation | 2022 |
| Ace ARK Consultancy Limited | Administrative & support | 2017 |
| Ace ARK Investments Limited | Real estate | 2020 |
| Ace IT Services Ltd | Information & communication | 2017 |
| Ace Logistics Delivers Ltd | Transport & logistics | 2025 |
| Ace MAN & Van Couriers Ltd | Transport & logistics | 2023 |
| Ace MAN & Van Removals Ltd | Transport & logistics | 2023 |
| Ace PCO Rentals Ltd | Administrative & support | 2024 |
| Ace Physiotherapy Ltd | Health & social care | 2012 |
| Acetutorplus LLP | | 2023 |
| Acewise Limited | Other services | 2015 |
| Acham Akuj Limited | Real estate | 2023 |
| Achitei Ltd | Construction | 2016 |
| Achyuta Technology Ltd | Other services | 2023 |
| Acious Limited | Professional & scientific | 1970 |
| Acit Services Ltd | Information & communication | 2024 |
| Ackrya IT Solutions Ltd | Information & communication | 2017 |
| ACL 2014 Holdings Limited | Professional & scientific | 2014 |
| ACL 2025 Holdings Ltd | Financial services | 2025 |
| ACL Holdings Group Limited | Real estate | 2024 |
| ACL Site Services Ltd | Construction | 2019 |
| Acme Trading Corporation Ltd | Wholesale & retail | 2018 |
| ACN Home Care Service Ltd | Administrative & support | 2019 |
| Acooper Sales Ltd | Wholesale & retail | 2025 |
| Acorn (Watford) Ltd | Health & social care | 2006 |
| Acorn Abodes Ltd. | Real estate | 2017 |
| Acorn Experiences Limited | Education | 2015 |
| Acorn Freight Limited | Transport & logistics | 2025 |
| Acorn PVT Ltd | Wholesale & retail | 2025 |
| Acorn Renewables Ltd | Energy | 2021 |
| ACP Realisations Limited | Manufacturing | 2002 |
| Acps Ventures Ltd | Hospitality | 2022 |
| Acquarius Consulting Ltd | Professional & scientific | 2013 |
| Acre H Ltd | Real estate | 2021 |
| Acrotrix Edinburgh Ltd | Education | 2025 |
| Acrotrix Global Ltd | Administrative & support | 2025 |
| Acrotrix Hornchurch Ltd | Education | 2025 |
| Acrotrix Ltd | Arts & recreation | 2019 |
| Acrotrix Watford Ltd | Arts & recreation | 2022 |
| Acs-Apt Computer Systems Limited | Information & communication | 1989 |
| Acta Homes Ltd | Health & social care | 2024 |
| Actaeon Advisors Ltd | Professional & scientific | 2018 |
| Acte in UK Ltd | Professional & scientific | 2024 |
| Action for Children | Health & social care | 2003 |
| Action for Children Developments Limited | Health & social care | 2009 |
| Action for Children Pension Trustee Limited | Financial services | 1952 |
| Action for Children Services Limited | Health & social care | 1989 |
| ACTIV8 Distribution Holdings Limited | Financial services | 2012 |
| ACTIV8 Distribution Limited | Wholesale & retail | 2000 |
| Active Air Engineering Ltd | Energy | 2024 |
| Active Investors Group Ltd | Education | 2024 |
| Active Sporting Communities CIC | Education | 2016 |
| Activehaven UK Ltd | Health & social care | 2020 |
| Activeselect Limited | Administrative & support | 2024 |