| Jacobs Clean Energy | Knutsford, Cheshire East, Warrington | 14 | 11 |
| Integrated Decommissioning Solutions | Middlesborough, Cumbria, Whitehaven | 9 | 11 |
| Jacobs | London, Knutsford, Cheshire East | 5 | 62 |
| Cavendish Nuclear | Warrington, Bristol, Cumbria | 9 | 8 |
| NSG Environmental | Chorley, Aldermaston, London | 7 | 6 |
| Tradebe Inutec | Dorchester, Dorset, Marlow | 6 | 3 |
| Mott Macdonald | Copeland, Croydon, Liverpool | 5 | 60 |
| Cyclife | Cumbria, Workington, Allerdale | 5 | 5 |
| Cumbria Nuclear Solutions | Workington, Cumbria | 10 | 12 |
| Augean | Near Wetherby, York | 8 | 3 |
| Atkins | Cumbria, Moor Row | 6 | 128 |
| Nexus | Manchester | 4 | 5 |
| Abbot Risk Consulting | Glasgow, Edinburgh | 3 | 3 |
| Stork Technical Services RBG | Aberdeen, Dyce | 3 | 3 |
| AECOM | London, Plymouth | 2 | 137 |
| Mirion Technologies Canberra | Didcot, Harwell Campus | 2 | 4 |
| Energy & Compliance Technology | Wakefield | 2 | 2 |
| Galson Sciences | Oakham | 7 | 11 |
| Nuvia | Warrington | 4 | 4 |
| Akins | Moor Row | 4 | 4 |
| Suez | Fylde | 3 | 3 |
| Tuv Sud | Glasgow | 2 | 10 |
| Q5 Partners | London | 2 | 6 |
| Golder Associates | Nottingham | 2 | 3 |
| Lloyds Register Quality Assurance | London | 2 | 2 |
| Hayward Tyler | East Kilbride | 2 | 4 |
| Veolia | Ellesmere Port | 2 | 2 |
| Amentum | Warrington | 2 | 2 |
| Envision Engineering & Design | Thurso | 2 | 2 |
| Moore Medtech | Wetherby | 2 | 2 |
| Nuclear Decommissioning | Preston | 2 | 2 |
| Wood | Knutsford | 2 | 2 |
| Deloitte | London | 1 | 122 |
| XMA | Nottingham | 1 | 93 |
| WSP | Manchester | 1 | 132 |
| Arcadis | London | 1 | 79 |
| PA Consulting Services | London | 1 | 54 |
| Microsoft | | 1 | 24 |
| Frazer Nash Consultancy | Dorking | 1 | 32 |
| Wood Environment & Infrastructure Solutions | Knutsford | 1 | 13 |
| Whale Tankers | West Midlands | 1 | 11 |
| NCC Group Security Services | Manchester | 1 | 11 |
| Korn Ferry | London | 1 | 9 |
| Adt Fire & Security | Manchester | 1 | 11 |
| Flyform | Cardiff | 1 | 7 |
| Glasgows | Leyland | 1 | 7 |
| Mitchell Diesel | Sutton in Ashfield | 1 | 6 |
| Arup | London | 1 | 79 |
| NSSL Global | Redhill | 1 | 13 |
| DBD | Warrington | 1 | 6 |
| Kellogg Brown & Root | Leatherhead | 1 | 3 |
| Tet | London | 1 | 3 |
| Cumbria County Council | Cumbria | 1 | 3 |
| Thurston Group | Wakefield | 1 | 3 |
| Electro Motive Diesel | Doncaster | 1 | 2 |
| Orano Projects | Abingdon Oxon | 1 | 2 |
| Peterson | Aberdeen | 1 | 2 |
| Adapt | Cumbria | 1 | 7 |
| CNSL | Cumbria | 1 | 3 |
| Circular 1 Health | Carlisle | 1 | 2 |
| Decommissioning Alliance | Wokingham | 1 | 2 |
| Jacobs Stobbarts | London | 1 | 2 |
| M5Tec | Newton Aycliffe | 1 | 2 |
| 89 47996 | Southwark | 1 | 1 |
| Abbot Risc Consulting | Edinburgh | 1 | 1 |
| Abbott Risk Consulting | Edinburgh | 1 | 1 |
| Acclaim Training | Cumbria | 1 | 1 |
| Acorn Coaching & Development | Cumbria | 1 | 1 |
| Acs | Bradford | 1 | 1 |
| Active Collection Bureau | Maidstone | 1 | 1 |
| Afnor | Birmingham | 1 | 1 |
| Altrad | Merseyside | 1 | 1 |
| Arlington Fleet Services | Eastleigh | 1 | 1 |
| Asbestos Compliance | Frodsham | 1 | 1 |
| Ashley Management Services | Hale | 1 | 1 |
| Augean Treatment | Wetherby | 1 | 1 |
| Aw Stokes | West Bromwich | 1 | 1 |
| Baxter Neumann Leadership Solutions | Knutsford | 1 | 1 |
| Bendalls Engineering | Carlisle | 1 | 1 |
| Berwicks | Edinburgh | 1 | 1 |
| Brimstone Enterprises | Barrow in Furness | 1 | 1 |
| Cabot Norit | Glasgow | 1 | 1 |
| Cavendish | Warrington | 1 | 1 |
| Celadon Decommissioning KDC | Manchester | 1 | 1 |
| Community Organisers | Warminster | 1 | 1 |
| Contec Design Services | Thurso | 1 | 1 |
| Costain Oil Gas & Process | Manchester | 1 | 1 |
| Cumbria Nuclear Soloutions | Cumbria | 1 | 1 |
| Decommissioining Alliance | Wokingham | 1 | 1 |
| Designhive Media | Compton | 1 | 1 |
| Doosan Power Systems | Esher | 1 | 1 |
| Ecology by Design | Chalgrove | 1 | 1 |
| Emcel Filters | Horsham | 1 | 1 |
| Equiniti Group | Crawley | 1 | 1 |
| FRS Contractor Solutions | Penarth | 1 | 1 |
| Gleeds Energy | London | 1 | 1 |
| Graham Engineering | Nelson | 1 | 1 |
| Hargreaves Jones | Manchester | 1 | 1 |
| Hireserve | Basingstoke | 1 | 1 |
| Hugh Simpson Contractors | Wick | 1 | 1 |