I work at a small convenience store in the UK and I was recently informed that I failed a test purchase (I sold someone who was under 18 a vape cartridge). I understand that I'm in deep shit, however aside from being told that I'll have to redo all my training, no one has really told me what to expect in the coming days. The shop manager is currently off on a 2 week holiday and so he obviously hasn't been in to explain this stuff to me. Instead, I have received numerous conflicting bits of information as to the severity of the penalty. From some I've been told that I definitely won't be sacked, however others have told me that I probably will be. Some have said that I'll probably be let off with a warning since its my first fail, whereas others have said I'll probably have to pay a hefty fine and may even get a criminal record.

I just need someone to clarify things for me so I know just how deep the shit is that I'm in. So again to be clear, I sold someone who was under 18 a vape cartridge. I'm from the UK. I have never failed a test purchase before. What sort of penalty should I expect?