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| Company Name | County | Tel: No. |
| D D Lamson Plc | Hampshire | 023-9258-4271 |
| David Terry Packaging Engineering Co. | Dyfed | 01554-835511 |
| Deamco Corp Ltd. | Surrey | 01483-579889 |
| Deecon Engineering (Bilston) Ltd. | West Midlands | 01902-408553 |
| Digitron-Translift Ltd. | Nottinghamshire | 01777-707511 |
| Don Valley Engineering Co. Ltd. | South Yorkshire | 01302-322101 |
| Dorvic Engineering Co. Ltd. | South Yorkshire | 0114-248-5633 |
| Duct Engineering (Luton) Ltd. | Bedfordshire | 01582-562626 |
| Dunn Systems Ltd. | Leicestershire | 01530-414444 |
| Dynamic Air Ltd. | Buckinghamshire | 01908-568155 |