You can send them privately with Parcelforce Express48.
https://www.parcelforce.com/help-and-advice/sending/prohibitions-and-restrictions
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"All firearms other than low powered air weapons."
"Low powered air weapons, together with pellets and other airgun and airsoft projectiles, can be sent subject to the 3 conditions stated."
My point again, that my initial post was "You can send Co2 cartirdges privately with the 48 hour service. Once more to iterate, I was not talking about pressurized magazines.
In the grid it states weapons and ammunition. Gas is neither it is the propellant.
In the link it states this:
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You might want to look into finding yourself a new eye doctor as there is nothing in that section about gas containers or co2 capsules, Technically i am not even sure it covers gas guns at all as it only states low powered air weapons although its unlikely they would know the difference. It includes lead pellets and airsoft projectiles but nothing about co2 capsules.
My eyes are fine, please try and read once more that I was talking about Co2 capsules and my post reflects this. ? smh