| Allergen.Io Limited | Stoke-On-Trent | 2025 |
| Allergens Made Easy Ltd | Dunfermline | 2026 |
| Allergic Media Limited | Isleworth | 2025 |
| Allergotech Limited | Reading | 2013 |
| Allergy Advisor App Ltd | Banbury | 2025 |
| Allergy AID Ltd | London | 2024 |
| Allergy Ecosystem Limited | Carshalton | 2017 |
| Allergy Fluent Ltd | London | 2025 |
| Allergy Menu Limited | Stoke-On-Trent | 2017 |
| Allergypath Ltd. | Marlborough | 2025 |
| Allerkarn Limited | London | 2022 |
| Allerton Consultancy Limited | Leeds | 2020 |
| Allerton Grange Services Limited | Whitehills Business Park | 2007 |
| Allerton I.T. Consulting Ltd | Liverpool | 2020 |
| Allerton Music Ltd | London | 2023 |
| Allerton Partnership Ltd | London | 2016 |
| Alles Klar Ltd | Bromborough | 2020 |
| Alletak Ltd | Epsom | 2018 |
| Allevate Limited | Twickenham | 2007 |
| Alleviate IT Solutions Ltd | Wakefield | 2024 |
| Alley Cat Games Ltd | London | 2016 |
| Alley Games Ltd | London | 2025 |
| Alley Tech Ltd | London | 2023 |
| Alleycat Consultancy Limited | Cheadle | 1994 |
| Alleycat Projects Ltd | London | 2024 |
| Alleycats Features - Lost Boys Ltd | Londonderry | 2019 |
| Alleyneslens Ltd | London | 2026 |
| Alleyo C.I.C. | Warrington | 2015 |
| Allez Productions Ltd | Hove | 2026 |
| Allezcat Ltd | London | 2023 |
| Allfiled UK Limited | Southampton | 2008 |
| Allfiliate Ltd | Uckfield | 2016 |
| Allfilm Limited | Sheffield | 2024 |
| Allflyghts Ltd | Birmingham | 2025 |
| Allfocal Optics Limited | Oakham | 2022 |
| Allform Labs Limited | Stoke-On-Trent | 2026 |
| Allforprojects Limited | Halesowen | 2026 |
| Allforum.Com Limited | Warminster | 2000 |
| Allfour Technologies Limited | Shirley | 2019 |
| Allfunds Data Analytics Limited | London | 2014 |
| Allgains Limited | Maidstone | 2025 |
| Allgebras Ltd | London | 2022 |
| Allgigs Limited | Maidstone | 2004 |
| Allgis Ltd | London | 2026 |
| Allgood AI Ltd | London | 2025 |
| Allgoose Ltd | Glasgow | 2017 |
| Allgosystems Ltd | Bristol | 2025 |
| Allgrove Consultancy Limited | Bournemouth | 2015 |
| Allguard Payments Limited | London | 2024 |
| Allhandit Limited | Maldon | 2012 |
| Allhorse International Limited | Weybridge | 2019 |
| Alli Intelligence Ltd | Bolton | 2025 |
| Alli YOU Need Limited | London | 2017 |
| Alliance Automation Limited | Bolton | 2022 |
| Alliance Builders Ltd | Leigh | 2019 |
| Alliance Business Computers Limited | Barnsley | 1983 |
| Alliance Business Solutions Ltd | Slough | 2016 |
| Alliance Capital Partners Limited | Egham | 2016 |
| Alliance Communications Ltd | Dummer | 2005 |
| Alliance Communications Solutions Limited | Dummer | 1998 |
| Alliance Computer Holdings Limited | Barnsley | 1996 |
| Alliance Development Ltd | London | 2025 |
| Alliance Digital Corporate Banque Ltd | London | 2022 |
| Alliance Diversified Ltd. | Addiscombe Road | 2002 |
| Alliance Document Solutions Limited | Barnsley | 1996 |
| Alliance Document Systems Limited | Maidstone | 2012 |
| Alliance Films (UK) Development Limited | London | 2011 |
| Alliance Films (UK) Limited | London | 1997 |
| Alliance for Cohesion and Racial Equality Ltd | Reading | 2012 |
| Alliance for Public Awareness | Coventry | 2014 |
| Alliance Integrators Ltd | London | 2024 |
| Alliance Knights IT Limited | Hornchurch | 2021 |
| Alliance Media Limited | London | 2014 |
| Alliance Media Partners International Limited | Egham | 2016 |
| Alliance Media Partners Limited | Egham | 2015 |
| Alliance News IS (Italian Service) Limited | London | 2017 |
| Alliance News Limited | London | 2013 |
| Alliance Omnichannel Limited | London | 2021 |
| Alliance Park Ltd | Watford | 2017 |
| Alliance Prime Accounting and Tax Consultancy Ltd | London | 2024 |
| Alliance Publishing Press Limited | London | 2011 |
| Alliance Publishing Trust | London | 2006 |
| Alliance Solutions Group Limited | Maidstone | 2004 |
| Alliance Solutions Limited | Maidstone | 2000 |
| Alliance Strategies Limited | Berkshire | 2002 |
| Alliance Support Limited | Maidstone | 2004 |
| Alliance Systems Ltd | Leighton Buzzard | 1996 |
| Alliance Technical Support Services Limited | Brandon | 2002 |
| Alliance Telecom Ltd | Edinburgh | 2010 |
| Alliances (BMC) Limited | Cardiff | 2024 |
| Alliances Intelligence Ltd | Camberley | 2025 |
| Alliant Audio Ltd | Radstock | 2019 |
| Alliant Cyber Security Ltd | Taunton | 2023 |
| Alliant Digital Limited | Feltham | 2024 |
| Alliant Solutions Limited | Taunton | 2025 |
| Alliantist Limited | Brighton | 2003 |
| Allianz Facialities Ltd | London | 2026 |
| Allianz Facilities Ltd | London | 2026 |
| Allicom Consultancy Limited | Manchester | 2022 |
| Allicsurd Limited | Taunton | 2023 |