| 1C Properties Limited | Pembroke Dock | 2025 |
| 1C Property Developments Limited | London | 2024 |
| 1CALL Construction & Builders Ltd | Slough | 2020 |
| 1CALL Roofing + Building Ltd | Sutton | 2025 |
| 1CAPITAL U.K Limited | Birmingham | 2020 |
| 1COLD Ltd | Redditch | 2005 |
| 1CORE Electrical Solutions Ltd | Tadley | 2023 |
| 1DD Limited | Barnet | 2019 |
| 1DS Projects Ltd | London | 2022 |
| 1ECO Solutions Limited | Burnley | 2026 |
| 1EIGHTY Roofing Solutions Limited | Malvern | 2015 |
| 1F Investments Ltd | Belfast | 2017 |
| 1GCC Limited | Sheffield | 2002 |
| 1GLF Limited | Birmingham | 2019 |
| 1GREEN (Leicester) Limited | Nottingham | 2024 |
| 1HORIZON Design and Build Limited | Northampton | 2021 |
| 1J Improve Your Home Ltd | Kilmarnock | 2022 |
| 1K1 Limited | Bristol | 2014 |
| 1KAL Apartments Ltd | Bradford | 2024 |
| 1KE London Ltd | Ballymena | 2020 |
| 1LIFE London Limited | London | 2004 |
| 1LPM Limited | Greenford | 2022 |
| 1M Project Services Ltd. | Alresford | 2019 |
| 1M Property Development Limited | London | 2014 |
| 1MB Cabling Solutions Limited | Halesowen | 2008 |
| 1MLV Limited | London | 2020 |
| 1N Developments Ltd | Orpington | 2019 |
| 1NA (Draycott) Limited | Nottingham | 2023 |
| 1NA (Hollington) Limited | Nottingham | 2022 |
| 1NA (Melton) Limited | Nottingham | 2013 |
| 1NA (Olive Grove) Limited | Nottingham | 2023 |
| 1NE Group Limited | Houghton Le Spring | 2018 |
| 1NG Limited | Newcastle Upon Tyne | 2009 |
| 1NG Utilities Ltd | Manchester | 2025 |
| 1NTEGRATED Ltd | Watford | 2023 |
| 1OAK Homes Ltd | Luton | 2019 |
| 1OAK Projects Limited | Newcastle | 2024 |
| 1OFF Homes Ltd | West Wickham | 2018 |
| 1ONES Construction Ltd | Newark | 2022 |
| 1PANDPC Ltd | London | 2024 |
| 1PJ Limited | Nottingham | 2025 |
| 1PM Construction Ltd | Ilford | 2018 |
| 1PSG Ltd | Whyteleafe | 2024 |
| 1R Construction Limited | Basildon | 2022 |
| 1RAVSON Ltd | Cambridge | 2021 |
| 1S Capital Group Ltd | Swansea | 2021 |
| 1SCAFF LAB Ltd | Witham | 2020 |
| 1SERVCO Ltd | West Hampstead | 2021 |
| 1SM Ltd | Hove | 2026 |
| 1SOURCE ALL Trade Solutions Ltd | Glasgow | 2026 |
| 1SPACEPROJECTS Limited | Weston-Super-Mare | 2017 |
| 1ST & 2ND FIX Mechanical & Electrical Services Ltd. | Dundee | 2017 |
| 1ST & 4MOST Solutions Ltd | Tamworth | 2003 |
| 1ST 4 Electrical Installations Limited | Westbury | 2012 |
| 1ST 4 Electrical Services Ltd | Bristol | 2006 |
| 1ST 4 GAS Limited | Nuneaton | 2020 |
| 1ST 4 GAS Services Ltd | Bradford | 2025 |
| 1ST 4 Plumbing Ltd | Stevenage | 2006 |
| 1ST 4 Roofing Services Limited | Bristol | 2014 |
| 1ST 4 Services (UK) Ltd | Henley-In-Arden | 2012 |
| 1ST 4 Windows Limited | Wetherby | 2006 |
| 1ST Ability Limited | Leeds | 2009 |
| 1ST Able Building & Maintenance Limited | Mexborough | 1997 |
| 1ST About Plumbing & Carpentry Ltd. | Rochester | 1990 |
| 1ST Accurate Services Ltd | Woodford Green | 2003 |
| 1ST Action GAS & Heating Limited | Cradley Heath | 2016 |
| 1ST Active Property Services Limited | Chislehurst | 1998 |
| 1ST Advanced Access Limited | Ashton-Under-Lyne | 2009 |
| 1ST Advanced Groundworks Limited | Hindhead | 2020 |
| 1ST Advanced Heating & Plumbing Limited | Lancing | 2010 |
| 1ST Advanced Heating Limited | Hindhead | 2002 |
| 1ST Advanced Scaffolding Systems Limited | Carlisle | 2002 |
| 1ST Alert UK Limited | Cardiff | 2003 |
| 1ST Architects London Limited | Norwich | 2012 |
| 1ST Architects Ltd | Nottingham | 2009 |
| 1ST Arrow Services Ltd | Hampton | 2013 |
| 1ST Aurora Limited | Accrington | 2006 |
| 1ST Avenue GAS Ltd | Bushey | 2025 |
| 1ST Aylesbury Plumbing & Heating Limited | Aylesbury | 2009 |
| 1ST Aztec Limited | Bristol | 2005 |
| 1ST Base Piling Solutions Ltd | Wigan | 2018 |
| 1ST Benchmark Limited | Worksop | 2018 |
| 1ST Boiler Care Ltd | London | 2022 |
| 1ST Boilers Limited | Benfleet | 2015 |
| 1ST Brick Limited | Tipton | 2023 |
| 1ST Building Contractors Limited | Gravesend | 2015 |
| 1ST Building Renovator Limited | London | 2022 |
| 1ST Call 24-7 Ltd | Pershore | 2011 |
| 1ST Call Construction Ltd | Cannock | 2019 |
| 1ST Call Construction Maintenance and Repair Ltd | London | 2025 |
| 1ST Call Contractors Limited | Borehamwood | 2025 |
| 1ST Call Electrical Services Limited | Gillingham | 2001 |
| 1ST Call Electrical Services North West Limited | Prenton | 2010 |
| 1ST Call Engineers Limited | Coventry | 2020 |
| 1ST Call Flame Heating Limited | Bristol | 2009 |
| 1ST Call GAS Services Limited | Sheffield | 2004 |
| 1ST Call Glass Care Ltd | Norwich | 2004 |
| 1ST Call Glass Ltd | Southend-On-Sea | 2021 |
| 1ST Call Glazing Limited | Mitcham | 2003 |
| 1ST Call Group Ltd | London | 2019 |