Gases, including flammable, non-flammable, toxic and compressed gases (including new, used and empty gas cylinders, ethane, butane, refills for lighters, fire extinguishers and scuba tanks, life jackets, nitrogen dioxide and carbon dioxide canisters including culinary foaming devices & soda stream)
All flammable compressed gases are prohibited* e.g. blowlamps; butane; lighters and refills containing flammable liquid or gas; ethane; gas cylinders for camping stoves; hydrogen; methane and propane.
All toxic compressed gases are prohibited* e.g. chlorine; fluorine etc.
All non-flammable compressed gases are prohibited* e.g. air bags; scuba tanks, carbon dioxide; fire extinguishers; neon and nitrogen.
Empty cylinders that are sealed so that residual gas under pressure are prohibited,
only those cylinders which are open to the atmosphere for inspection are permitted
*includes new, used and empty gas cylinders
https://personal.help.royalmail.com/...onal-customers
If it has a buddy bottle or removeable cylinder and the valve is out and open to the atmosphere then it can be sent .