Clockwise to close.

[Oliver Buckle]

It's ingrained, every nut and bolt, every bathroom tap, clockwise to close. So why do the people who make taps for plastic water butts do it the other way around. It is really annoying, I have left a tap open on an empty butt and lost the next lot of rain, if I had 10p for every time I have done it I might be able to buy a chocolate bar.

 

[Meadowlark]

Interesting. The only lefthand fitting I've encountered here is the propane fitting. It is called POL (prest-o-lite) and its reason for being is to prevent accidental cross connection with something that should never mix with propane.

You can’t accidentally screw a propane connector into a water line, airline, or standard plumbing fitting because those are always right‑hand threaded here.

I've never seen it on nor have ever used a water butt...that would be confusing for sure. I wonder why they used it on water butts?

 

[Oliver Buckle]

You are right, in the UK gas fittings have a left hand thread so you can't connect mains gas to water. It's not really a thread on the taps, just a basic hole one side, blocked off the other, so a full half turn turns it off or on.
I have one barrel that is some sort of industrial waste barrel, that has a hole drilled and a proper brass tap fitted. The others are made to fit with a fairly coarse screw thread on the hole and the tap.
Another problem, screw the tap into the barrel tight enough to seal, and have the tap facing downward at the same time, luckily I have a good selection of washers.