You need to pass immigration and reclear security unfortunately. As you arrive from LHR you do not end up in the terminal but in the corridor before immigration.

I've never transferred non-schengen to non-schengen at ARN though I'm fairly sure there is no transfer option that avoids immigration and security.

Sorry, that is BS. ARN arrivals (like HKG in the future or EWR/ORD today) in the F pier can connect to LHR (or other non-schengen) flights without any need to enter Sweden/Schengen. Some arrivals need to go thru security because the origin country doesn't comply with EU security standards.

And if the flight from London to Arlanda arrives at a non F gate? Is there an option to get to the F gates without entering Schengen? It has been a while since I did that but back then it seemed.that there where no options but to go through passport control.

A call button for airside transfer by van/bus to get from non-F to F?

The non-F to F bus doesn't put you behind "Schengen"/upstairs F-pier where you are boarding your HKG flight.

I'm sure Oliver2002 is right, I just don't know where you make the turn back to the F-pier? When you arrive from outside Schengen you are let out in the upstairs corridor which funnels you to the immigration booths. After immigration there is a security check-point to immediately enter F-pier again. I've just never noticed a different means to stay on the non-Schengen side (because I've never needed it).

And like CPH-Flyer states, not all non-Schengen arrivals use F-pier. I've had multiple flights from LHR and SPU put me on the other immigration check-point above the regular gates.

The airside transfer is from T2 to T5. I am talking about arrivals at non F gates in T5. You exit the plane and are sent above the gates to an immigration check point. Unless they changed something, I don't think there is an alternative to immigration.

There is. Theorectically you can connect from TG/ET/CA arrivals in T5B to T5F. It will take a while, because border police will need to fetch a transport option, but in the end it can be done.

I'm flying back from EWR next Wednesday and will have a look to clear up the confusion.

Thanks for all replies so far.

I'm not worried about entering Schengen as I have an EU passport, although if I don't need to enter then I won't. But if I do enter then I'll need to exit again right away, which seems a bit odd

This is what I'm getting at. Are arrivals from LHR treated as secure? Basically this will impact what I carry in my hand luggage if I don't need to unpack it during transit. Also, I want to access the *G lounge which may change things

Are arrivals from EWR treated as secure? If LHR is, and EWR isn't, then it won't help with my question although it would clear up whether there is an obvious route to stay airside without passing through immigration

EWR and LHR are both "secure" points of origin. Not sure that it helps you.

They are so thinly staffed at some times of day during parts of the year that even with a call option I'm not so sure that they always have a free body to do the escort to always deliver on schedule for all such routing possibilities where the connection may meet the airport MCT. Perhaps they can, but I'm not sure that they always can.

If you want to access the lounge, the question of entering the Schengen area or not becomes moot. There is no lounge is in the non-Schengen area.

Many thanks. So LHR is treated as a secure origin, but the lounge is inside Schengen. I assume the lounge is within the secure area?

Now back to my original question which I'm still not entirely clear about. My trip to ARN will be:
1. arrive from LHR
2. enter Schengen
3. go to *G lounge
4. exit Schengen
5. board flight to HKG.

Will I need to go though security at any of these points?

Yes, right after #2. When you pass immigration there is a check-point to your right which lets you re-enter terminal 5.

There are clear signs indicating it.

ARN Connecting
 

Connecting ARN with 2 separate tickets on July 22:

BOS-FRA-ARN LH800 Arriving at 9:15am

ARN-OSL SK849 Departing at 11:00am

Is this enough? I have never visited Scandinavia......