The VRSM was instituted with effect from 1 April 1999 to replace the separate medals that used to be issued to personnel of the separate Reserve Forces, including the Territorial Decoration and Efficiency Medal (Territorial) for the Territorial Army.
Reserve personnel are eligible for award of the VRSM after 10 years reckonable service in the Reserve Forces, provided that they have earned training bounty as required by their obligatory training commitment as defined in individual service regulations in 9 out of the 10 qualifying years.
Up to 5 years former regular service may count as half qualifying time, giving a maximum of 2 and a half years eligible service. Complex regulations apply to the use of former service and periods of Full Time Regular Service (FTRS) and Non Permanent Regular Service (NPRS) as qualifying time towards the VRSM.
Source: MOD