It's not about a defence, I know it would be their fault. They wouldn't know this. I don't care, I'm the one likely on the floor injured with a knackered irreplaceable bike worth thousands and lose fitness that would take weeks if not months to get back depending on the injury - could be more fatal.
It matters re the overtake as there is a big difference in gap required to legally pass a single cyclist compared to two with a gap in between them. It's the difference between being able to overtake and not being able to do so on many roads. If you're casually doing this chatting to your mate in z1/z2 expect the vehicle driver to be annoyed and confrontation. Why would you want to waste your time with this when out riding?
I've said similar before, why should the cyclist like myself, at an elevated heart rate, sometimes drastically so, with a mixture of adrenaline and fatigue and exposed to the elements be the one who makes the decision on what is or isn't a safe overtake? This is as opposed to the vehicle driver sat on their arse at a resting heart rate with none of the other drawbacks.
From what I've heard and seen, the cyclists who get the abuse or worse are the ones who ride defensively and think they're in control. You aren't, even if the law dictates you're in the right. There's only one winner, and that's the vehicle should you get hit. I show them respect and side with them even if they're wrong as a result.
I agree, my own experiences are that sticking deliberately out two abreast obtusely feels very wrong, I always tuck in when going through the twisties in an incline (I'm slower) so if cars suddenly come accross me mid bend, I'm maximising the escape room, and when cars are behind, I'll tuck in too, allowing them plenty of 'safe' overtaking opportunities.. What I don't do is stick out like a sore thumb and rely on drivers being on the ball, I feel more in control by creating the safe overtaking situation etc..
And having been teaching my daughter to drive and living at the edge of the Cotswolds, it's a regular occurrence to happen upon cyclists. I cycle myself, ride motorbikes and drive, so I tend to be sympathetic towards all road users, however it's eye opening with a new driver to see how much harder it is in reality to overtake cyclists riding two abreast, not only may it be miles before the road is wide enough, but when just wide enough, it takes much more care positioning the car as you are juggling 2M of clearance to the cycles to the right hand verge, distracting you from overtaking, which arguably means never overtaking if people want to get pendantic about 'safety'..
Of course, no surprise that most cyclists riding two abreast choose to flout the new rules themselves "on quiet roads or streets, moving over to the left if a faster vehicle comes up behind them, but only if they can do so safely"..
Honestly I think the new rules are stupid, they are deliberately causing more conflict IMO on both sides, Cyclists who act ignorantly and selfishly, as well as cars that expect them to now pull over when they are approaching, it sounds like the exact opposite of working together.