An interesting situation.
I am a specialist adviser in my present role and have to work to the 'plain English' rules when writing policy. There should be no doubt about what my policy is stating and who it applies to.
From what I have read, the UK HSE have not made the situation clear and obvious to the reader. A FAIL in my humble opinion. Unlike the Australian regulations that appear to treat the X-Ray machine as highly hazardous and so heavily controlled throughout its life. No such action in the UK or ebay would not be able to post auctions involving such equipment.
However, I have little doubt that if someone phoned the Ionising Radiation advisers at the HSE, they would 'play Safe' and say that ANY user of ionising radiation comes under the act. I suspect, however, provided a user is an individual with appropriate knowledge of using X-Ray equipment (as am I) then they will have better things to do with their time than chase every secondary market buyer of X-Ray equipment in the UK. There is certainly plenty of such kit for sale, much of it is the far more hazardous open X-Ray source type.
A most interesting situation but I certainly do not intend to open Pandoras Box and if the HSE are kept as busy as I am as an adviser, I suspect they would not thank me raising it with them ! Unless working with others (as an employer) I would suggest common sense applies.
Many weird and wonderful things happen inside peoples garages. Provided a person does not act irresponsibly and attract unwelcome attention, the authorities remain relatively disinterested. I speak from a position of knowledge
In the UK we are overstretched and have bigger fish to fry. Just do not go asking us for official comment as that is when we HAVE TO lay down the law. And no I have no connection with the UK HSE.
Aurora