Trade unions
M
| Full Name | Short Name | Notes |
|---|---|---|
| Machine and General Labourers' Union | MGLU | |
| Managerial and Professional Officers | MPO | |
| Manufacturing Science Finance | MSF | |
| Marine Workers' Union | MWU | |
| Medical Practitioners Union | MPU | |
| Merchant Seamen's League | MSL | |
| Midland Textile Association | Midland Text Ass | |
| Miners Federation of Great Britain | MFGB | |
| Musicians Union | MU |