Medicament delivery device with permanent locking of release button

A power pack for a medicament delivery device, comprising:

• a tubular body extending along a longitudinal axis from a proximal end to a distal end, wherein the tubular body includes a first protrusion which extends radially inwards from an inside wall of the tubular body and includes a first contact surface facing towards the proximal end;
• and
• a release button at least partially arranged within the tubular body and movable in relation to the tubular body along the longitudinal axis, wherein the release button includes a flexible arm extending towards the proximal end, wherein an end of the flexible arm includes a second protrusion extending radially outwards from the flexible arm and circumferentially aligning with the first protrusion, wherein the second protrusion includes a second contact surface facing towards the distal end,
• wherein
• the release button further includes a third protrusion closer to the distal end along the longitudinal axis than the second protrusion and extending radially outwards from the flexible arm, circumferentially aligning with the second protrusion and including a third contact surface facing towards the distal end, or
• the tubular body further includes a third protrusion closer to the proximal end along the longitudinal axis than the first protrusion and extending radially inwards from the inside wall of the body, circumferentially aligning with the first protrusion and including a third contact surface facing towards the proximal end, and
• wherein the flexibility of the flexible arm allows the release button to be pushed in the proximal direction along the longitudinal axis to at least a first position and a second position closer to the proximal end along the longitudinal axis than the first position, such that with the release button at the first position, a removal of the release button from the tubular body by pulling or pushing the release button towards the distal end is blocked by the first contact surface abutting the second contact surface, and such that with the release button at the second position and with the third protrusion included as part of the flexible arm, a pulling or pushing of the release button along the longitudinal axis towards the distal end and towards the first position is blocked by the first contact surface abutting the third contact surface or, with the release button at the second position and with the third protrusion included as part of the tubular body, a pulling or pushing of the release button along the longitudinal axis towards the distal end and towards the first position is blocked by the second contact surface abutting the third contact surface.