| Alliants Limited | Professional & scientific | 2009 |
| Allied Chlorin Limited | Wholesale & retail | 2004 |
| Allied Office Machines Limited | Wholesale & retail | 2002 |
| Allied Services Ltd | Information & communication | 1998 |
| Allied UK Property Services Ltd | Construction | 2019 |
| Allinonesurveys Limited | Professional & scientific | 2015 |
| Allka Ltd | Wholesale & retail | 2025 |
| Allocate Property Group Ltd | Households | 2025 |
| Alloy Automations Ltd | Information & communication | 2026 |
| Alloy Wheel Clinic Limited | Wholesale & retail | 2022 |
| Alloy Wheel Repair Southampton Ltd | Manufacturing | 2018 |
| Alloy Wheels Repair Ltd | Other services | 2022 |
| Allset Transport Ltd | Transport & logistics | 2026 |
| Allstars MB Ltd | Wholesale & retail | 2026 |
| Allukev Ltd | Hospitality | 2025 |
| Allways Transfer Ltd | Transport & logistics | 2024 |
| Ally Law Security Ltd | Wholesale & retail | 2026 |
| Allyn Court Management Company Ltd | Real estate | 2003 |
| ALM Property Enterprise Ltd | Real estate | 2026 |
| Almacomposites Ltd | Manufacturing | 2013 |
| Almarin Trans Ltd | Transport & logistics | 2019 |
| Almo Power Ltd | Construction | 2012 |
| Almond Removals Ltd | Transport & logistics | 2023 |
| Almosawi Smile Limited | Health & social care | 2024 |
| Almuhtaseb Vision Limited | Health & social care | 2020 |
| ALN Electrical Services Ltd | Construction | 2016 |
| ALN Property Ltd | Real estate | 2021 |
| Alni Group Ltd | Transport & logistics | 2019 |
| Aloe Vera Pro Ltd | Wholesale & retail | 2019 |
| Aloequine LLP | | 2006 |
| ALP Learning Solutions Ltd | Education | 2022 |
| Alpaca Legal Services Ltd | Professional & scientific | 2026 |
| Alpha 1 Maintenance Limited | Construction | 2022 |
| Alpha Bravo Trading Limited | Wholesale & retail | 2024 |
| Alpha Brew Ltd | Manufacturing | 2025 |
| Alpha Cleaning Group Ltd | Administrative & support | 2024 |
| Alpha Consultancy MS Limited | Professional & scientific | 2023 |
| Alpha Consulting Limited | Education | 2025 |
| Alpha Coop African Groceries Ltd | Wholesale & retail | 2024 |
| Alpha CRM Limited | Information & communication | 2013 |
| Alpha Electrical Systems Limited | Manufacturing | 1989 |
| Alpha Healthgroup Ltd | Health & social care | 2018 |
| Alpha PA Limited | Professional & scientific | 2011 |
| Alpha Resource UK Ltd | Administrative & support | 2009 |
| Alpha Resources (UK) Limited | Extraterritorial | 2012 |
| Alpha Smith Limited | Administrative & support | 2016 |
| Alpha Systems Consultants Ltd | Information & communication | 2002 |
| Alpha Tattoos Ltd | Professional & scientific | 2022 |
| ALPHA33 Cars Ltd | Wholesale & retail | 2018 |
| ALPHACARE24 Ltd | Health & social care | 2023 |
| Alphacom Solutions Ltd | Other services | 2025 |
| Alphadent Laboratories Ltd | Health & social care | 2016 |
| Alphalink Visionary Network Ltd | Wholesale & retail | 2024 |
| Alpine Building Developments Limited | Professional & scientific | 2013 |
| Alpine Computer Equipment Limited | | 1983 |
| Alpine Continuity Solutions Ltd | Information & communication | 2026 |
| Alpine Elements Limited | Administrative & support | 2003 |
| ALR Electrical Services Ltd | Construction | 2015 |
| Alresford Marquee Hire Limited | Administrative & support | 1995 |
| Alresford Motor Services Limited | Wholesale & retail | 2000 |
| Alresford Town FC Limited | Arts & recreation | 2020 |
| Alrusu Freight Ltd | Transport & logistics | 2025 |
| Alrv Services Limited | Hospitality | 2023 |
| ALS Digital Ltd | Professional & scientific | 2020 |
| Alsephina Limited | Real estate | 2021 |
| Alsephina Lodges Ltd | Hospitality | 2025 |
| Alsurike | Real estate | 2021 |
| ALT Designer Ltd | Construction | 2025 |
| ALT Investment Limited | Financial services | 2014 |
| Alta BNB Ltd | Hospitality | 2026 |
| Altair IP Ltd | Professional & scientific | 2018 |
| Altair Management Limited | Households | 2023 |
| Altair RE Investment Limited | Real estate | 2023 |
| Altan Education & Language Consultancy Services Ltd | Professional & scientific | 2018 |
| Alter Horizon Enterprises Limited | Information & communication | 2017 |
| Alternative Cruise Parking Limited | Transport & logistics | 2015 |
| Alternative Pubs Group Limited | Financial services | 2021 |
| Alternative Security Limited | Administrative & support | 2026 |
| Altertek Ltd | Manufacturing | 2005 |
| ALTF4GROUP UK Limited | Administrative & support | 2022 |
| Altoria TM Services Ltd | Construction | 2026 |
| ALU Gripper Marketing Limited | | 1991 |
| Alum Homes Ltd | Construction | 2017 |
| Aluminium Windows Ltd | Construction | 2013 |
| Alumni of Maritime Academy of Nigeria Oron, Europe (Amano Europe) Ltd | Administrative & support | 2021 |
| Alvatek Ltd | Professional & scientific | 2007 |
| Alveier Limited | Financial services | 2013 |
| Alvolt Energy Ltd | Energy | 2020 |
| Always Checkers Publishing Ltd | Information & communication | 2025 |
| Always Flourishing International Ltd | Administrative & support | 2014 |
| Always Landscaping Ltd | Administrative & support | 2024 |
| Always Plastic Free Ltd | Wholesale & retail | 2018 |
| ALY & Co Limited | Transport & logistics | 1998 |
| Alyboss Ltd | Transport & logistics | 2024 |
| Alymaxy Ltd | Administrative & support | 2016 |
| ALZ Trans Ltd | Transport & logistics | 2019 |
| AM Antiques Limited | Wholesale & retail | 2017 |
| AM Machining Ltd | Manufacturing | 2016 |
| AM Marine UK Holdings Ltd | Professional & scientific | 2025 |
| AM Signs & Engraving Ltd | Manufacturing | 2015 |