Well, I have no idea whether something along the lines of a "Cake Bakery - this is for food additives only" section would be a workaround or not (in a vape store, online or B&M)...
Thing is, if they want to slap tax on it (whatever liquid), you're not just up against trading standards, you're up against the much more powerful & scary HMRC.
In the event of let's say a tax on nicotine liquids, coupled with a restriction flavours allowed, I know that many vape stores would stock nic shots, and have a "bakery food flavouring" section.. and just see what happens...
But we're dealing with so many unknowns here, and how those restrictions will correlate...
e.g. in the event of flavour restrictions, will all flavours have to fulfil new criteria and be passed by the MHRA (or other) again, in order to be allowed to be placed on the market?