I am going from ARN (on SK) to SFO (on UA) via LHR. If I remember correctly the SK flight arrives at T3(?) which is the same terminal as the UA flight to SFO departs from. I just heard a rumouer that even when you are on transit at the same terminal, you have to go through a new security screening at LHR.

Anybody on this experienced forum who knows the facts?

yes indeed that is true.
when transitting at LHR you have to go through security once again with two lines for transfer: one for T1,2&4 (where transit security is performed at the receiving terminal) and another for T3 (which unfortunately is usually very long and understaffed - so allow plenty of time for transit)

Yes, you have to reclear security at LHR when transiting there like you are. T3-T3 transfers have been bad for me during the morning, mid-day and early afternoon -- particularly as they eat into my lounge use time.

What is the sanity behind that rule?

Security at Heathrow is bad pretty much everywhere nowadays, so allow plenty of time at the airport.
And yes, you always have to go through security when passing the airport, even on transit. Follow the signs marked "Flight Connections" and you will sooner or later end up at a security control.

Both SAS and UA use terminal 3, so fortunately no need to take a bus as is the case if you have to transfer to any of the other three terminals at LHR.

Also keep in mind that if you transit in the UK the UK rules for hand luggage apply, so it's strictly one piece of hand luggage. If you have two bags or the one you have is too large you will be forced to check the bag, so do check the exact rules before you leave.
Unfortunately they enforce this strictly!

If the lines for transfer security are long, you may want to go through arrivals immigration then departure security, particularly if you hold an EU passport (immigration will be fast). I have done this in the past and plan to do it again when I transit LHR next week. Transfer security lines can be really long compared to departure security.

Justin

Very true, although there are some times that are exceptions to that. For T3-T3 or T3 to other terminals, I sometimes check out the transfer line and then if I don't like it, I head landside. For EU member state nationals, this should be easy enough .... and it even (generally) works for others who don't need a visa to enter the UK.

Thank you guys for sharing your experiences regarding todays LHR security procedure for transit passengers. Your advises have been of great value for me.^

Not to rain on the 'head landside' parade, but I just got home from T3 and the queue to get back airside was very, very long. If you've flying C or F on UA then that's a good idea as you can use Fast Track......otherwise that may be a problem.
Sadly when airside there's no way of knowing how long the queues are...

As I wrote in another thread, last time I passed LHR in December it took over 45 mins to get past security, the entire first floor (landside) was just a long queue, I have never seen anything like it!!!

The fast track helps a bit though, but you need a C or F BP to use it, status won't give you access.

Well I have a C ticket and EU passport so if there are long qeues at transit security, it is probably worthwhile to go out through immigration and back through Fast Track. Thanks.

You should check out LHR T2 security landside-to-airsed checkpoint in the early morning. Between 5 to 6 a.m. I routinely see how bad LHR can be, for it's amongst the worst lines witnessable at LHR right there. (And Terminal 2 needs a demolition-renovation IMO.)

It could be a good idea, but that's assuming you know LHR well as LHR (and T3 in particular) is not the most logical of airports and can get confusing.
Also keep in mind that even the fast track is not as quick as it used to be, expect up to 10-15 mins in worst case during peak periods.

I haven't been to T2 for a long time, but I've heard the security there is notoriously bad these days.
It used to be very quick, less than 5 mins to get through security during many of my visits in the past, I guess the good days are over...
I agree it's a terrrible terminal, easily the worst and ugliest at LHR.

The predictions I have read on this page, are very pessimistic...

I haven't transferred T3/T3 since end of September, (transferred 4 times in September, 2 times in August after the liquid ordeal) I have never experienced more than 15 minutes wait at the transfer security check point. UA has representatives pulling 1K/C pax out of the line and help you get up front.

If the line turns out to be enormous, go land side and use the fast track.

Please report back on how transfer was

I've done a few ARN-LHR-ORD (T3-T3) flights in the past two months (on my ways N, NW of you; not NE or I'd end up in the water ), and the transit was no fun. I have been stuck there for well over 30 minutes on each and every one of those Sunday mid-day transits there. I'll have to go back to my records to tell you exactly how long I was stuck airside for T3-T3 on midday Sundays, but it was always more than 30 minutes for me these recent past Sundays. (Can I really be that unlucky? )

On the second most recent such trip for a T3-T3, I even saw people (who don't need a visa to enter the UK) being turned away from doing a landside transit. That was quite a bit of a shocker to me and I hope that doesn't become increasingly standard or that'll eat up even more time (as one goes from the immigration line back to the security line, which may well be longer by the time one returns). Of course for you good old boys with EU passports, that shouldn't be an issue.