Regardless of what the law says, I find it discouteous.
It's perfectly legal to walk three-abreast along the pavement, but if a little old lady is coming the other way with her shopping trolley, it's kind, courteous and thoughtful to move into file while she passes.
The argument that 'a passing car should allow as much space as it does for a car' can lose something in real life.
If we are arguing that a car must allow a single cyclist the same room they allow a car, does that mean a whole lane?
That is the width I allow for a car when I'm passing it in my car.
That being so, do I then allow two whole lanes for two cyclists riding abreast?
If not, do I allow them the width I'd give a car plus the width of one bicycle?
This is a serious question, not some exercise in elementary trolling.
In the lanes around my picturesque market town, passing a single bicycle is fraught with difficulty. I know. I train regularly on those lanes; so do my two younger children, who still live at home.
Passing two cycles abreast is a practical impossibility unless they go in line astern.
I ride 2-abreast with my children along the lanes, but as soon as we hear a car we slip into line. It's a common courtesy.
On most roads, I would not even consider riding two-abreast.
"Because the HC says I can" just seems the weak justification of the kind of cyclist who refers to motorists as 'motons'.
But I'm lucky. In 40 years cycling and 30 years driving, I've never had a cross word with another motorist or cyclist. Maybe if I'd been unfortunate enough to elicit quite unjustified insults from other road users, I'd be more inclined to hang with my grimy fingertips onto the hallowed word of the HC. I don't know.
