| ALT-PPA1 Limited | Worcester | 2021 |
| Alta Design & Development Limited | Cardiff | 2018 |
| Alta Electrical Solutions Limited | Scarborough | 2026 |
| Alta Facilities & Estates Maintenance Limited | London | 2019 |
| Alta Homes (Finstock) Ltd | Oxford | 2026 |
| Alta Roofing Ltd | Huddersfield | 2024 |
| Alta Vista Construction Limited | Newcastle Upon Tyne | 2017 |
| Alta Vista Global Limited | Cleveland | 2006 |
| Altaclara (Bramshot) Ltd | West Horsley | 2019 |
| Altaclara (Loampit) Ltd | West Horsley | 2019 |
| Altaclimate Limited | Shrewsbury | 2020 |
| Altacon Ltd | Claudy | 2021 |
| Altaf Capital Developments Ltd | Manchester | 2025 |
| Altaf Ltd | Bradford | 2024 |
| Altaform Limited | Cardiff | 2018 |
| Altaglobe Ltd | Edinburgh | 2024 |
| Altair Acquisitions Limited | Worthing | 2010 |
| Altair Building Limited | London | 2004 |
| Altair Construction & Development Limited | Stonehaven | 2013 |
| Altair Geological and Environmental Services Ltd | Diss | 2026 |
| Altair Group Developments Ltd | Tamworth | 2025 |
| Altair Group Limited | Tamworth | 2024 |
| Altair Roofing Ltd | Barnsley | 2025 |
| Altam Construction Ltd | London | 2023 |
| Altam Limited | London | 2016 |
| Altamira Services Ltd | Basildon | 2026 |
| Altan Plumbing & Heating Ltd | Swansea | 2021 |
| Altar Construction & Building Projects Ltd | Maidenhead | 2023 |
| Altar Construction Limited | London | 2025 |
| Altara Property Group Ltd | London | 2026 |
| Altarstone Ltd | Newcastle Upon Tyne | 2025 |
| Altaven Group Limited | London | 2026 |
| Altavia Homes Ltd | Portsmouth | 2014 |
| Altay Steel Limited | Grantham | 2019 |
| Altay Tech Ltd | London | 2025 |
| Altcom 407 Limited | Salford | 2006 |
| Altcon Ltd | York | 2017 |
| Altcor Construction Ltd | Truro | 2019 |
| Altea Construction Ltd | Borehamwood | 2023 |
| Altea Contracts Limited | Burgess Hill | 2024 |
| Altea Engineering Ltd | London | 2026 |
| Altec Consultants Ltd | London | 2020 |
| Altec Facades Ltd | Luton | 2022 |
| Altec Services Ltd | Liverpool | 2019 |
| Altech Electrical Limited | Woodhall Spa | 2021 |
| Altech Electrical Services Ltd | Crieff | 2014 |
| Altech North West Limited | Heswall | 2003 |
| Altek Group Ltd | London | 2020 |
| Alteku Ltd | London | 2016 |
| Altemont Asset Management Limited | Winchester | 1993 |
| Altenergy Community Investments Limited | Taunton | 2023 |
| Altenergy Limited | Taunton | 2021 |
| Altenergy.Life Ltd | London | 2025 |
| Alteo Builders Ltd | Romford | 2023 |
| Alter & Native (DM) Limited | Harrow | 2025 |
| Alter & Native Ltd | London | 2019 |
| Alter Air Ventilation Ltd | Basildon | 2018 |
| Alter Artistry Ltd. | London | 2019 |
| Alter Construction Limited | Slough | 2014 |
| Alter Eco Renewables Limited | Nantwich | 2023 |
| Alter Fitout Limited | London | 2019 |
| Alter FM Ltd | Ongar | 2021 |
| Alter GM Ltd | Nottingham | 2019 |
| Alter Image (Oak Designs) Limited | Tonbridge | 2003 |
| Alter Interiors Limited | West Molesey | 2002 |
| Alter Landscapes Limited | Renfrewshire | 1991 |
| Alter-Ego Joinery and Construction Ltd | Glasgow | 2017 |
| Alter-House Ltd | Reading | 2016 |
| Altera (PVT) Limited | Hemel Hempstead | 2025 |
| Altera Design & Build Ltd | Barnsley | 2025 |
| Altera Ltd | Redhill | 2025 |
| Alterations, Renovations & Demolitions Ltd | Leeds | 2020 |
| Altercity Properties Limited | Borehamwood | 1998 |
| Altered Carbon Heating and Cooling Ltd | Bedford | 2020 |
| Altered Estates Limited | London | 1998 |
| Altered Images (Contractors) Limited | Uxbridge | 1999 |
| Altered Images (Decorators) Limited | Nottingham | 2016 |
| Alterego Building Projects Limited | London | 2016 |
| Alterego Construction & Interiors (Consultancy) Ltd | Glasgow | 2006 |
| Altering Images Ltd | Hailsham | 2022 |
| Alterior Limited | Hemel Hempstead | 2003 |
| Alteriors Design and Build Ltd | Bristol | 2020 |
| Alterity Developments Limited | Altrincham | 1987 |
| Altermore Builders Ltd | Longfield | 2019 |
| Altermore Limited | Swanscombe | 1982 |
| Alterna Renewables Ltd | Sheffield | 2024 |
| Alternate Construction Limited | Esher | 1990 |
| Alternate Energy UK Ltd | Livingston | 2013 |
| Alternative Access Services Ltd | Kirkcaldy | 2019 |
| Alternative Access, Rigging & Scaffold Solutions Limited | Blackpool | 2017 |
| Alternative Alterations Ltd | Ramsey | 2021 |
| Alternative Bedrooms Limited | Romford | 2007 |
| Alternative Building Services Southern Limited | Havant | 2015 |
| Alternative C F Electrical Ltd | Dundee | 2023 |
| Alternative Cooling Solutions Limited | Loughborough | 2001 |
| Alternative Energy Contracting Ltd | Bishop Auckland | 2006 |
| Alternative Energy Products Limited | Banbridge | 2009 |
| Alternative Energy Solutions (Shropshire) Limited | Telford | 2011 |
| Alternative Energy Solutions Limited | Abingdon | 2010 |
| Alternative Finishes Limited | Wakefield | 1999 |