Lowering soil pH

I think it is potentially toxic to soil organisms, and as it's already soluble I can't imagine it would have any long lasting effect.

I think one of the sulphates is ericaceous - iron, I think?

I'm using Chempak "chip grade sulphur" on my blueberries because the pH has crept back up to neutral since I planted them 5 or so years ago.

Like flowers of sulphur (which I couldn't get, but would probably work quicker) it is broken down by soil bacteria into various acidic sulphites and acids, but it does take several months, and doesn't really happen at all in cold soil conditions.
It probably works best if mixed well into the soil, which is a bit tricky with blueberries as they are rather shallow rooted.

Too early to say whether it's working for me, but it's the only "proper" treatment I could find in my researches.

A mulch of pine needles or peat moss can help as they both release organic acids as they rot down, and ammonium sulphate is an acid-forming fertiliser which can be watered in, although it's only really a source of nitrogen.

I would think that any sort of vinegar would only be a very temporary fix and might have unexpected side effects.
If your soil contains free lime it will always try to "buffer" the pH upwards whatever you do so in that respect no treatment could be considered "permanent."

Just from my old (shaky school) chemistry knowledge, any organic and mineral acid should neutralise lime, in the case of vinegar forming calcium acetate. However opinion seems to confirm that applying it may burn the roots of the plant and in any case majority opinion is that it only will lower pH for a couple of days which is useless.But how can soil pH which has been lowered leap up again unless you apply more lime?

Vinegar is a very dilute solution of acetic acid so doesn't have the ability to dissolve (and therefore eventually "lose") large amounts of lime, unless added regularly in industrial quantities!
Most soils contain some lime which will continue to try to reverse any attempts at acidification until it's all used up (especially if added to by using tap water, particularly in hard water areas.)

I've read about sulphur, and the concensus opinion is that it's one of the best long lasting remedies for neutralising lime and eventually reducing soil environment to an acidic pH (<7). Only trouble is it's about the slowest remedy. It can take at least a couple of years to have an effect.

Hope not - I got the impression that it should start to take effect within a few months in warm soil conditions, although it could well require repeat applications over a long period of time to make big pH changes.