Remedy that worked extremely well:
Wash area stung with soap and warm water. Apply neat TCP(see below).
The pain was effectively gone in a couple of hours, about six hours
later the welts were gone too.

This was the treatment I applied after I had received a really bad
second sting in two days. I was about 100m out body surfing, and had
popped about half a dozen blue bottles (I assume they sink when the
air sac is popped - maybe not, and this is why I got stung).  I am
always careful when surfacing after diving under a wave as I am really
scared of getting stung near my eyes, but this one got me while I was
swimming (head up, water-polo style) against the sidewash in clear
water. It got me across my cheek, neck, chest, under the arm and
across the shoulder blade. I scraped it off furiously for a few
seconds (never did see the air sac) then struck off for the beach. I
had had a bad sting two days before (see below) so was worried that I
might get a limb seizure as I had previously.

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*** THIS IS RECOMMENDED IF YOU WANT THE FULL DETAILS OF THE REMEDY ***

Once on land I asked at the life-guard tower for some vinegar (this is
provided at beaches at the Great Barrier reef for same - I will quote
an article tomorrow that claims this is ineffective, which suggested
meat tenderizer instead {I remember when I was a child my father used
to say use paw-paw skin, apparently some enzyme therein helps}). The
life guards had a tube of white cream, I asked to see what it was, the
name was not memorable - something pretty generic and uninformative. I
most remember them asking me to leave the tower as I was dripping on
their floor!

I made speed back to the holiday flat, fortunately only a few minutes
fast walk. By now my cheek and underarm were stinging violently. Once
there I did not try any of the previous remedy that had not worked,
instead took a warm bath and soaped off all the stinging areas. On a
whim I tried neat TCP, applied liberally to all these areas.
TCP is an antiseptic product produced by Pfizer Laboratories,
containing
6% Chlorinated Phenol
2% Phenol (Isn't this the stuff mothballs are made of - it certainly
smells thereof)
1% Iodinated Phenol
½% Sodium Salicylate.

I am not sure whether it was the soapy wash or the TCP, but the
results were dramatic compared with the previous treatment I
attempted. As I said above, 6 hours later no pain and no marks.

The previous sting referred to above, occurred when walking at the
surf's edge on the beach. Being aware of blue bottle presence, I was
watching out for them, and had been fishing them out and burying them.
A lifeguard's opinion was that the stinging tails remain active for
about 12 hours after removal from water - any one have corroboration
of this or alternative information?

Anyway, out of the blue I got a stinging tail wrapped around my ankle.
The first priority was to get this off - no sticks or implements
around so I scoured it off with sand (the article I will cite tomorrow
also says this is a no-no, what else can one do though?). Then I got
some ice from a beach vendor and held this on for about 10 minutes.
The latter is my universal treatment for all injuries bar frost-bite,
and generally it works very well, particularly for cuts, burns,
bruises, insect bites etc.

So I sat on the beach, watching everyone else continue swimming in
blue bottle riddled water (as I was to do myself too, prior to the
incident above) waiting for my remedy to take effect. Well it didn't,
I started developing a mild seizure in my hamstring and also began to
feel dizzy. I stuck this out for about 45 minutes, with the side
effects getting worse, then decided to get back to flat. I doused it
with methiolate there (a mercurochrome based product) and had a few
cups of warm sugary tea, but it took most of the day before I felt up
to doing anything, and it was painful for a couple of days.

The contrast between the two recoveries astounded me. I realise one
probably gets variation in virulence between bluebottles, but given
the initial pain of the later sting being as much, if not more,
pronounced than the sting on my ankle, I doubt this could explain the
different reactions.

The final anecdote I have was the only other time I had a serious blue
bottle sting - the tail wrapped a couple of times round my forearm. I
don't think I put anything on that, if anything it was only something
like Dettol. I can't remember how long the stinging lasted, but the
welt was visible for 8-10 days.