A medicament delivery device for delivering a liquid medicament, the medicament delivery device comprising: a rigid casing containing a deformable medicament container, the deformable medicament container arranged to contain the liquid medicament; a pressurized gas cartridge connected to the rigid casing via a gas valve; wherein the gas valve is releasable to allow gas flow into the rigid casing to cause an increase in gas pressure in the rigid casing so as to compress the deformable medicament container to displace the liquid medicament.