| Alternative Management Limited | Wolverhampton | 2010 |
| Alternative Minds Limited | Maidenhead | 2004 |
| Alternative Point Ltd | Rye | 2010 |
| Alternative Property Income Venture (General Partner) Limited | London | 2006 |
| Alternative Resolution Administration Ltd | London | 2016 |
| Alternative Resources Limited | Shepperton | 2000 |
| Alternative Solutions Group Ltd | London | 2025 |
| Alternative Spectrum Consultancy Services Limited | Northampton | 2026 |
| Alternative Strategies (U.K.) Limited | Kettering | 2003 |
| Alternative Travel Group (Holdings) Limited | Oxford | 1985 |
| Alternative Vehicles Technology Limited | Somerset | 2003 |
| Alternative Water Company Ltd | Wakefield | 2026 |
| Alternative Water Supply Company Limited | Ashford | 2008 |
| Alternatives (GB) Limited | Wokingham | 2011 |
| Alterniq Inspired Growth Ltd | London | 2020 |
| Alterniq Limited | London | 2011 |
| Alternis Mediation Limited | Harrogate | 2023 |
| Alternity Limited | London | 2019 |
| Alternox Scientific Ltd | Brighton | 2020 |
| Altero Blue Ltd | London | 2025 |
| Alterra Capital Advisors Limited | Watford | 2004 |
| Alterra Capital America Limited | London | 2010 |
| Alterra Capital Brazil Limited | London | 2010 |
| Alterra Capital UK Limited | London | 2006 |
| Alterstone Ltd | Cambs | 2007 |
| Altes Services Ltd | London | 2024 |
| Altet Automotive Limited | London | 2025 |
| Altet Services Limited | London | 2024 |
| Alteva Group Limited | London | 2025 |
| Altevo Energy Ltd | North Shields | 2024 |
| Altevus Ltd. | Peterborough | 2024 |
| Alteya Ltd | London | 2022 |
| Altezza People UK Limited | Stafford | 2021 |
| Altfinch Civil Engineering Limited | Liverpool | 2013 |
| Altgate Ventures Ltd | London | 2024 |
| Altgen Ltd | Glasgow | 2023 |
| Altgott and Simpson Group Limited | London | 2023 |
| Altham Aviation Ltd | Fleet | 2016 |
| Altham Lewis Architects Limited | Sutton | 2013 |
| Althara Corporate Ltd | Egham | 2025 |
| Altharom Limited | London | 2017 |
| Althea Rose Ltd | Harlow | 2022 |
| Altheome Limited | London | 2025 |
| Altheon Digital Ltd | Edgware | 2025 |
| Alther Solutions Ltd | Wilmslow | 2018 |
| Althera Ltd | Boston | 2022 |
| Altheus Engineering Ltd | Nottingham | 2022 |
| Althie J Ltd | Croydon | 2016 |
| Altho DAI Ltd | Newcastle Upon Tyne | 2023 |
| Althorne Project Consultants Ltd | Redhill | 2022 |
| Althorpe Designs Ltd | London | 2020 |
| Although Digital Ltd | Newmarket | 2022 |
| Althrix Ltd | Barking | 2026 |
| Altias Holdings Limited | Finchley | 2015 |
| Altiba Ltd | Lyndhurst | 2021 |
| Altibury Ltd | Altrincham | 2019 |
| Alticec | Wigan | 2026 |
| Altico Studio Ltd | Lancaster | 2013 |
| Alticor Ltd | London | 2018 |
| Alticore Access Ltd | South Shields | 2026 |
| Altidoc Ltd | Wadebridge | 2025 |
| Altier Tech Ltd | Newton Abbot | 2023 |
| Altieye Limited | Kington | 2025 |
| Altify UK Employee Option Plan Limited | London | 2022 |
| Altilitech Ltd | Plymouth | 2020 |
| Altilium Clean Technology Ltd | Plymouth | 2022 |
| Altilium Ltd | Plymouth | 2022 |
| Altilium Metals Ltd | Plymouth | 2020 |
| Altima Branding Limited | London | 2017 |
| Altima Consulting Ltd | London | 2025 |
| Altima Partners Limited | London | 2026 |
| Altimaro | Cardiff | 2023 |
| Altimise Ltd | Wimborne | 2017 |
| Altimist Ltd. | London | 2023 |
| Altimmune UK Limited | Leeds | 1992 |
| Altimus Consulting Ltd | Tunbridge Wells | 2023 |
| Altimus Group Ltd | Basildon | 2026 |
| Altimus.Com Limited | Leamington Spa | 1996 |
| Altin Ltd | Birmingham | 2022 |
| Altinvet Peripatetic Cardiology Specialist Ltd | Marlow | 2025 |
| Altion Law Limited | Cranfield | 2010 |
| Altior Accountancy & Taxation Ltd | Cheltenham | 2022 |
| Altior Advisors Ltd | London | 2024 |
| Altior Asset Management Ltd | Cheltenham | 2020 |
| Altior Consulting Ltd | Cambridge | 2024 |
| Altior Finance Limited | London | 2019 |
| Altior Group Ltd | Leicester | 2025 |
| Altior Ltd | London | 2023 |
| Altior Solutions Limited | Edinburgh | 2017 |
| Altior Vocatio 241 Ltd | Billericay | 2023 |
| Altiora Advisory Group Limited | London | 2026 |
| Altiora Financial Ltd | Kilmarnock | 2026 |
| Altiora Leadership Limited | London | 2026 |
| Altiora Marketing Limited | Leominster | 2017 |
| Altiora Nexus Ltd | Egham | 2026 |
| Altiora Research Centre Ltd | London | 2025 |
| Altiorra Ltd | London | 2025 |
| Altios International UK Limited | London | 1996 |
| Altiplano Consulting Ltd | London | 2014 |
| Altiq (UK) Limited | London | 2009 |