Okay, that's fair enough. I thought it worth asking just in case there were any assumptions were being made (perhaps wrongly) about what options were available to you.
You will find if you go back to those shops and ask for a 12mm to 1/2 bsp tap connector they will have them!
2 reasons for not having what you asked for.
Plumbs and Grahams especially, have to find some stupid code and looking in the book they wouldn't have found your exact request - plus, some of the counter staff are daft!
The second is as you fear it is not a recommended connection. For reasons mentioned previously. Yes I have done it myself and yes it works.
I've got about 6 of these, unused, taking up shelf space in my shed, you're welcome to any of them for beer tokens if you can wait a couple of days for the post.
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