So apart from the wording of not crossing white lines, we're kind of agreeing with each other. This is from the highway code:
Double white lines where the line nearest you is solid. This means you MUST NOT cross or straddle it unless it is safe and you need to enter adjoining premises or a side road. You may cross the line if necessary, provided the road is clear, to pass a stationary vehicle, or overtake a pedal cycle, horse or road maintenance vehicle, if they are travelling at 10 mph (16 km/h) or less.
Laws RTA 1988 sect 36 & TSRGD regs 10 & 26
Another example, if you're following a scooter rider and you're on your bike in a 60 limit, and he's doing 40, you can pass him as long as you don't cross the white line. if it meant no overtaking then you couldn't. But if you do it and part of your mirror, handle bars, or panniers cross the white line then you're commiting an offence.
My God I'm even boring myself. I won't get onto why I believe you can cross them while filtering past traffic. That could just tip me over the edge.
Lol yeah I think we are on the same page, my only point for the Spain thing is you can’t cross the unbroken whites there, even to turn into a driveway etc 👍