IT'S ILLEGAL TO FILL IT IN THE UK............... doesn't matter if you use H-pac, dive tank or blow into it really hard. If it's in the UK then it's not been UK tested, therefore illegal to use it (it can't have been tested as it's not a UK standard......ask H-pac, but DO NOT use it)
Completely illegal and anyone trying to sell it to you is a dick. Unless it's from the US and even they should know better.
Health and Safety law, nothing to do with invalidating insurance.
So, before answering a question as serious as this, make sure you have the correct answer........... a newbie could take bad advice as gospel from someone with a high post count and bad information.
From the UKPSF site:
I have a DOT bottle can I use H-pac?
The simple answer is NO
H-pac will only fill HSE approved air cylinder that are in test. No other cylinders will be filled. This is the law in the UK.
So there you go, you can't fill a dot bottle in the UK.........same law for us as H-pac.