A medicament delivery device has a housing for a medicament container and a drive unit for a stopper in the container to expel a dose of medicament, the drive unit having a plunger rod and a dual back-to-back force spring assembly connected to the plunger rod； and a lock and release mechanism connected to the drive unit that has a hold member connected to the plunger rod, a rotator member connected to the hold member, and a tubular actuation member linearly slidable in relation to the housing and connected to the rotator member. The hold member is attached to the housing and has a generally tubular lock tube through which the plunger rod extends and two half-cylindrical seats for the dual back-to-back force spring assembly. The lock tube has a resilient lock and release device to interact with both the plunger rod and the rotator member.
