But the most important is the law on right of way. Turning traffic must give way to traffic going straight on (unless there is a right or left filter and the straight on traffic is stopped). This applies to both turning left and right. Further vehicles should only make a manoeuvre if safe to do so. A left turning car which cuts across a bike on its inside which is going straight on falls foul of these regulations.
And there's also a general rule not to overtake on the inside precisely because a vehicle outside you is not expecting it.
A cyclist should not be overtaking cars on the inside, which can easily happen in urban areas - cyclists are often the fastest vehicles on the road.
Firstly it is understandable that you didn't really understand the real example I gave a couple of days ago, because obviously you weren't there. But I was and much of what you say is either irrelevant or flat out wrong.
Firstly in my recent incident (one of many similar ones) I never overtook the car at all. The car overtook me and then when alongside me drifted into my lane (a bus lane) without indicating and then manoeuvred to turn left into a side street only at that point indicating left. This left me trapped on her inside and had I not been able to attract her attention she would have knocked my off my bike or worse.
It would be the equivalent of driving in the inside lane of a motorway and being overtaken by a car in the middle lane who while still alongside you moved into your lane without signalling to try to exit the motorway directly from the middle lane with a car on their inside. Except of course in that scenario the car is allowed in the inside pan, while in my incident the car isn't allowed in the lane I was in as it is a bus/cycle lane.
As a pointed out previously she did a whole raft of things that were wrong - I did nothing wrong.
But on your more general point you aren't right. The only time (well unless you are Bradley Wiggins) a bike is likely to be going fast enough to overtake a car is if the traffic is congested otherwise slowed, which as you indicate is often in urban areas. Where there are more than one line of traffic (which could of course include a line of cars and a separate line of bikes) and one line is moving slowly the Highway Code is absolutely clear that you can overtake on the left:
'stay in your lane if traffic is moving slowly in queues. If the queue on your right is moving more slowly than you are, you may pass on the left'
So a cycle is perfectly entitled to pass a line of stationary or slow moving cars on the left. Indeed the Highway Code also indicates in many places that this is likely to happen and for drivers (and indeed cyclists themselves) to be aware that bikes may be passing them (legitimately) on the left hand side e.g.
'In slow-moving traffic. You should ... be aware of cyclists and motorcyclists who may be passing on either side.'
'Use your mirrors and give a left-turn signal well before you turn left. Do not overtake just before you turn left and watch out for traffic coming up on your left before you make the turn, especially if driving a large vehicle. Cyclists, motorcyclists and other road users in particular may be hidden from your view.'
And there is a further point here relating to bus/cycle lanes. These are specifically designed to allow buses to pass more rapidly through traffic (and bikes allegedly more safety). These are nearly always on the left - if a bus in a bus lane (or a cycle) was not permitted to pass slow moving or stationary traffic on the left hand side there would be no point in having a bus lane in the first place as the buses would be forced to move at the speed of the rest of the traffic to avoid passing on the left.
On priority for traffic going straight on rather than turning, well the general rule is clear. Unless otherwise specifically indicated traffic continuing straight on on a main route has priority over traffic turning off that main route onto a minor route - and that applies whether turning right or left and for traffic going in the same direction or the opposite direction.
To suggest that a car turning left with a bike on its inside going straight has priority is the equivalent of saying that a car turning left off a motorway from the middle lane has priority over a car on its inside in the inside lane going straight on. This is non-sense and simply not correct.
But in my specific example the priority is even clearer (and again me in the right, her in the wrong). Remember I was in a bus/cycle lane and the Highway code specifically says:
'give way to any vehicles using a bus lane, cycle lane or tramway from either direction.'
