It is ambiguous, unless there are road markings just before where the camera car is?

My opinion is that Lane 3 at the lights becomes two lanes at the next set of lights, whereas Lane 1 goes into 1, Lane 2 goes into 2.

As usual, observation and anticipation would be the order of the day before any manoeuvre into an adjacent lane.

You state "you are approaching a roundabout from middle of three lanes" then post a picture of 4 lanes approaching a roundabout !

You should follow the road markings and be ready for other drivers not doing so. Don't rely on other drivers to do the right thing.

You (and the other party) both need to know where everyone else is and avoid them.

If it's about changing lanes, then the joiner is responsible for finding the gap. The difficulty here is that neither of you has any kind of priority and both are equally responsible for making a safe manoeuvre. In practice of course that should always be the case regardless of 'priority' if you want to avoid accidents.

Without seeing a video of what happened it's impossible to say whether one or both drivers took insufficient care or lacked skill. So it will go 50/50.

It's the sort of accident in which both drivers can probably say "it wasn't my fault" yet at least one of them could have avoided it.

Bad markings though. I'm sure something could be devised there to make things clearer.

I don't really mind Hangar Lane but it needs 100% concentration and there are always people who think that one flash of the indicator will make a gap for them and you need eyes in the back of your head, or a neck that swivels like an owl's.

Nothing new to say as I think everyone has covered it. really depend son the road markings, if there are none then

lane 1 is go 1st or 2nd exit, if first indicate left on the approach, if 2nd do not indicate on the approach but indicate left after first exit.

Lane 2 : Not for 1st exit, but 2nd or 3rd, If 2nd you have to check your inside mirror and move across to outer lane as soon as it is safe to do so, if 3rd exit then you should stay in lane until it is safe for you to move across but not before you have passed/opposite the 2nd exit.

Lane 3 : 3rd of 4th, indicating right on the approach, again checking that inside mirror before moving across to outer lanes.

MSM ~ Mirror Signal Manoeuvre.

The link does not work, general rule is that when changing lanes anywhere it is down to the car changing lanes to make sure it is safe to do so.

But as already stated it really depends on the road markings, or the signpost telling you which lane to be in on the approach to the roundabout. Sorry bescription is a little hard to follow.