| 1ST Class Heating Repairs Limited | Milton Keynes | 2003 |
| 1ST Class Installations Limited | Northampton | 2022 |
| 1ST Class Installs Ltd | Ashton-Under-Lyne | 2022 |
| 1ST Class Kitchens Limited | Chesterfield | 2005 |
| 1ST Class Partitions and Ceilings Ltd | Rotherham | 2018 |
| 1ST Class Plastering Ltd | Newton Abbot | 2019 |
| 1ST Class Plumbing Heating and Boiler Engineers Limited | Addlestone | 2017 |
| 1ST Class Reinforcements Ltd | Hornchurch | 2016 |
| 1ST Class Roof Company Limited | Tredegar | 2019 |
| 1ST Class Roofing & Building Ltd | Sheffield | 2012 |
| 1ST Class Roofing & Scaffolding Services Ltd | Leeds | 2021 |
| 1ST Class Roofing Limited | Stockport | 2025 |
| 1ST Class Scaffolding (Essex) Limited | Beckenham | 2015 |
| 1ST Class Scaffolding (South) Ltd | Havant | 2015 |
| 1ST Class Security Systems Ltd | Surrey | 2000 |
| 1ST Class Solutions Limited | Sheffield | 2020 |
| 1ST Class Systems Limited | London | 2023 |
| 1ST Class Tiling Ltd | Sheffield | 2022 |
| 1ST Class Tradesmen Ltd | Southend-On-Sea | 2014 |
| 1ST Class Windows Systems Holdings Limited | Bexhill | 2019 |
| 1ST Click Design & Build Ltd | Hayes | 2015 |
| 1ST Commercial FM Ltd | Swindon | 2025 |
| 1ST Commercial GAS & Mechanical Ltd | Swindon | 2019 |
| 1ST Communications Limited | Penarth | 2007 |
| 1ST Connect Plumbing & Heating Ltd | Sidcup | 2010 |
| 1ST Connection Networks Limited | Leeds | 2017 |
| 1ST Conservatory Centre Limited | Pontypridd | 2003 |
| 1ST Construction (NW) Ltd | London | 2024 |
| 1ST Construction Northwest Ltd | Manchester | 2019 |
| 1ST Contact Plumbing and Heating Limited | Bury St. Edmunds | 2013 |
| 1ST Container Conversion Limited | Rainham | 2026 |
| 1ST Cool Limited | Brentwood | 2003 |
| 1ST County Fencing Ltd | Dartford | 2022 |
| 1ST County Scaffolding Services Limited | Coventry | 2015 |
| 1ST Custom Development Ltd | Chatham | 2018 |
| 1ST Degree Heating and Plumbing Services Limited | Richmond | 2007 |
| 1ST Degree Limited | Hemel Hempstead | 2018 |
| 1ST Demolition Limited | Preston | 2019 |
| 1ST Design Construction Ltd | Deal | 2022 |
| 1ST Developments Chelsea Limited | London | 2017 |
| 1ST DIG Plant Hire & Construction Ltd | Kingswinford | 2026 |
| 1ST Direct Decoration Ltd | Ramsgate | 2009 |
| 1ST Direct Drainage Limited | Reigate | 2016 |
| 1ST Direct Glaziers Ltd | Colchester | 2024 |
| 1ST Double Glazing Doctor Scotbased Limited | Dunfermline | 2004 |
| 1ST Drainclear Limited | Chislehurst | 1995 |
| 1ST Dream Home Ltd | London | 2017 |
| 1ST Electrical Bristol Limited | Bristol | 2015 |
| 1ST Electrical Ltd | Newcastle Upon Tyne | 2024 |
| 1ST Electrical Services (UK) Limited | Bristol | 2005 |
| 1ST Electricare Limited | Bradford | 2019 |
| 1ST Electrics Ltd | Peterborough | 2024 |
| 1ST Estates Ltd | Grimsby | 2017 |
| 1ST Euro Services Limited | London | 2022 |
| 1ST Facilities Management Limited | East Brent | 2007 |
| 1ST Fire Solutions Ltd | Stroud | 2003 |
| 1ST Fire Systems Limited | Mansfield | 2020 |
| 1ST FIX Construction Ltd | Abingdon | 2023 |
| 1ST FIX Group Ltd | Gateshead | 2025 |
| 1ST FIX Mechanical Limited | Hornchurch | 2019 |
| 1ST FIX Plumbing & Heating Limited | Hornchurch | 2005 |
| 1ST FIX Property Ltd | Leicester | 2018 |
| 1ST FIX Services Ltd | Feltham | 2025 |
| 1ST FIX Upvc Ltd | Gateshead | 2022 |
| 1ST Fixings Electrical Services Ltd | Mitcham | 2018 |
| 1ST Flooring Limited | London | 2017 |
| 1ST Flooring Solutions Ltd | Solihull | 2020 |
| 1ST Folding Sliding Doors Limited | Greenford | 2004 |
| 1ST for Fencing (Erectors and Consultants) Limited | Melrose | 2010 |
| 1ST for Jobs & Access Limited | Galashiels | 2023 |
| 1ST for Resin Limited | London | 2023 |
| 1ST Forward Electrical Limited | Isleworth | 2015 |
| 1ST Foundations Ltd | Derby | 2004 |
| 1ST FSD Group Ltd | London | 2022 |
| 1ST Garage Doors Limited | Bournemouth | 2020 |
| 1ST GAS Heating Services Ltd | High Wycombe | 2021 |
| 1ST GAS Limited | Newark | 2016 |
| 1ST GAS Plumbing and Heating Limited | Woodford Green | 2025 |
| 1ST Glass Double Glazing Limited | Monmouth | 2003 |
| 1ST Glaze Direct Limited | High Wycombe | 2008 |
| 1ST Glazing Repairs Limited | Portsmouth | 2009 |
| 1ST Golf Construction Ltd | Horsham | 2014 |
| 1ST Green Electrical Ltd | Devizes | 2019 |
| 1ST Group Northeast Limited | Fraserburgh | 2024 |
| 1ST Grup Ltd | London | 2026 |
| 1ST Herts Ltd | Stevenage | 2006 |
| 1ST Home Design & Build Limited | Shipley | 2026 |
| 1ST Home Developments Ltd | Winsford | 2012 |
| 1ST Impressions (SW) Ltd | Exeter | 2023 |
| 1ST Impressions Home Improvements Ltd | Castle Street | 2014 |
| 1ST Impressions Painting & Decorating Ltd | Leeds | 2022 |
| 1ST in Energy Limited | Birmingham | 2013 |
| 1ST Independent Windows Limited | Kent | 2003 |
| 1ST Industrial Door Company Limited | Bournemouth | 1988 |
| 1ST Inrail Limited | Cheshire | 2007 |
| 1ST Insulation Ltd | Leicester | 2022 |
| 1ST Insulation Partners Limited | Wolverhampton | 1986 |
| 1ST Interiors Ltd | Nuneaton | 2008 |
| 1ST Investment Properties Ltd | Dagenham | 2011 |
| 1ST Kontact Limited | Bolton | 2002 |