| ALL Hands Yacht Management Software Ltd | Information & communication | 2026 |
| ALL Saints Hotels Limited | Hospitality | 2008 |
| ALL Saints Place Management Company Limited | Households | 2014 |
| ALL Things House Ltd | Construction | 2017 |
| All-Pak Engineering Holdings Limited | Financial services | 2019 |
| Alltech (U.K.) Limited | Agriculture & fishing | 1982 |
| Alltech E-CO2 Limited | Professional & scientific | 2009 |
| Alltech Farming Solutions (UK) Limited | Manufacturing | 2016 |
| Alltech's Beverage Division UK Limited | Professional & scientific | 2008 |
| Allwood Carpentry Ltd | Construction | 2012 |
| Almero Camden City LLP | | 2019 |
| Almero City Inc Crimscott LLP | | 2018 |
| Almonds - Penstar (Yaxley) Limited | Households | 2021 |
| Almonds - Penstar Limited | Real estate | 2019 |
| Aloha Foods Co Ltd | Hospitality | 2020 |
| Aluhome Ltd | Wholesale & retail | 2020 |
| Aluliving Ltd | Extraterritorial | 2020 |
| Aluminium Eco Solutions Limited | Construction | 2014 |
| Aluminium Eco Structures Ltd | Manufacturing | 2025 |
| Always Take Care Limited | Health & social care | 2010 |
| Amanda John Interior Design Limited | Professional & scientific | 2019 |
| Amazing PR Limited | Professional & scientific | 2004 |
| Amberstone Innovation Ltd | Professional & scientific | 2025 |
| Amrali Group Ltd | Financial services | 2026 |
| Amulet Solutions (Europe) Limited | Information & communication | 2006 |
| AMY Wilkinson Coaching Ltd | Professional & scientific | 2020 |
| Anand Shoes of Stamford Limited | Wholesale & retail | 2014 |
| Andjo Capital Limited | Real estate | 2014 |
| Andrew Spall Interim Ltd | Professional & scientific | 2023 |
| Andrews Landscaping Limited | Administrative & support | 2014 |
| Andy Bird Plumbing Ltd | Construction | 2015 |
| Andy Newton Cloud Consulting Ltd | Health & social care | 2018 |
| Andy Thorpe Limited | Administrative & support | 2022 |
| Angel Pubs Ltd | Hospitality | 2024 |
| Anglo American Letting Agency Limited | Real estate | 1999 |
| Anglo Integrated Systems Limited | Administrative & support | 2002 |
| Angry Dog Developments Ltd | Real estate | 2024 |
| Animal Matters Consultancy Ltd | Professional & scientific | 2020 |
| Anna Couture Alterations Ltd | Manufacturing | 2026 |
| Anna Couture Boutique Ltd | Wholesale & retail | 2026 |
| Anna Couture Brides Ltd | Wholesale & retail | 2022 |
| Anna Davies Wills and Estate Planning Limited | Professional & scientific | 2025 |
| Anna Wood Brand Solutions Ltd | Professional & scientific | 2019 |
| Anna's Attic Limited | Wholesale & retail | 2019 |
| Anson and Curtis Ltd | Hospitality | 2014 |
| ANT Advanced Engineering Ltd | Professional & scientific | 2024 |
| Anthony Beech Conservation Limited | Other services | 2019 |
| Antique Automobiles Invest Ltd | Wholesale & retail | 2019 |
| Anton Pubs Ltd | Hospitality | 2018 |
| Antony Knobbs IT Services Limited | Information & communication | 2013 |
| Apartstays Ltd | Hospitality | 2016 |
| Aperture Window Group Ltd | Construction | 2023 |
| Applegarth Partners Ltd | Financial services | 2018 |
| Appraise ME Limited | Information & communication | 2016 |
| Aqualoos Ltd. | Administrative & support | 2011 |
| Aquila Retreats Ltd | Real estate | 2026 |
| Arbprint Ltd | Information & communication | 2010 |
| ARC Financial Solutions Ltd | Professional & scientific | 2016 |
| ARC Tax Refunds Ltd | Professional & scientific | 2016 |
| Arcadia Estates (Kent) Limited | Real estate | 2016 |
| Arcadia Estates Limited | Real estate | 2016 |
| Arch Bespoke Joinery Ltd | Manufacturing | 2026 |
| Arch Label Agency Limited | Wholesale & retail | 2015 |
| Arctica Cost Management Limited | Professional & scientific | 2024 |
| Arctica Design Services Limited | Professional & scientific | 2024 |
| Arctica Limited | Construction | 1999 |
| Arctica Principal Designer Limited | Professional & scientific | 2024 |
| Arctica Solutions Ltd | Professional & scientific | 2023 |
| Armad Engineering Ltd | Construction | 2013 |
| Armad Scitech Limited | Wholesale & retail | 2024 |
| Armstrong Agriculture Limited | Agriculture & fishing | 2003 |
| Arraygrp Ltd | Manufacturing | 2021 |
| Arrowhead Industrial Services Limited | Professional & scientific | 1999 |
| Art of Slating Limited | Construction | 2013 |
| Artemis Exotics Ltd | Wholesale & retail | 2024 |
| Artisano Ltd | Hospitality | 2025 |
| Arvind Nivas Limited | Real estate | 2019 |
| ARX Alta Consulting Ltd | Professional & scientific | 2013 |
| AS Aero Ltd | Professional & scientific | 2023 |
| Asap Discounts Ltd | Administrative & support | 2009 |
| ASB Homes and Buildings Ltd | Real estate | 2024 |
| Ascari Race Cars Ltd | Manufacturing | 2021 |
| Asembo UK Limited | Other services | 2012 |
| Ashlington Ltd | Real estate | 2018 |
| Ashton Hand Surgery Ltd | Health & social care | 2010 |
| Aspect Energy Solutions Ltd | Construction | 2021 |
| Aspo Holdings Limited | Financial services | 2022 |
| Astek Dental Laboratory Limited | Health & social care | 1999 |
| Astrantia Management Ltd | Professional & scientific | 2009 |
| AT & a Barrett Limited | Transport & logistics | 2013 |
| Athena Studio Ltd | Other services | 2020 |
| Athene Communications Limited | Professional & scientific | 2003 |
| Athene Holdings Limited | Professional & scientific | 2004 |
| Atkins Procurement Services Ltd | Professional & scientific | 2014 |
| Atkins Property and Leisure Services Ltd | Real estate | 2018 |
| Atmospure Limited | Wholesale & retail | 2025 |
| Attunement Group Ltd | Extraterritorial | 2026 |
| Attunement Ledger Ltd | Information & communication | 2026 |
| Auction Rebel Limited | Wholesale & retail | 2018 |
| Aunby Farming Limited | Agriculture & fishing | 2025 |