Can someone please explain the security system at Heathrow to me? We (mother, partner and me) flew Dublin - Heathrow - San Francisco. We were screened by security in Dublin, were really in difficulty with connection time in Heathrow, but having come off a flight from Dublin (and still remaining airside) we had to go through security screening again at Heathrow before being allowed to board our plane! Having come off a flight from Dublin and remaining "airside", what security risk did we/could we pose?????????

First, it is common to having to go through security transiting between international flights. Amsterdam, Tokyo, etc... Nothing unique about LHR.

But because you're flying to the US, you'll go through an extra secondary screening specifically for US-bound flights along with a brief interview.

I accept it happens, but I still don't see the reason for it. If we've been cleared by security from Dublin to Heathrow, how can we pose any risk from thereon in if we remain "airside" ?

Because there are still different standards imposed by various airports around the world. LHR gets flights from all nations. Do you feel safe that you're on a flight next to someone who's only gone through security at some African, Middle-Eastern or Eastern-Europe airport?

Including some countries which regime actually sponsors terrorism around the world?

..the explanation is they don't have any way of segregating arriving transit passengers from "secure" places like Dublin from insecure places like wherever.....so all the time at Heathrow when you are transiting, even if you are not going into a new terminal but remaining within the same terminal, before you can get to a departure lounge you might go throw a security screening again.

Now also on all flights to the USA, there is another round of screening required bhy the paranoids in Washington who don't trust our allies to do a good job so at the gate, first one of the gate agents asks you several security questions upon collecting your boarding pass and then a security man, at least this is the way it's done on American, takes a look at your boarding pass and decides whether or not to order another search which will be a pat down and a hand search of your carryon...just how random this is is anybody's guess...I've been screened sometimes and other times not and have looked at the boarding pass to see if there are any special notations for the secondary check.

Travellers from Canada who pass through US airports, and then fly to Europe must go through both immigration and security

OK - to look at it another way - why should ANY country (UK, Ireland, USA, or any others) assume securirty in another country is adequate. It amazes me that many aiports don't re-screen people who are connecting airside.

We once trusted other countries' security. The incompetent Germans, and the even more incompetent American management of PanAm, showed us how unreliable that was, and 300 people were murdered over Lockerbie as a result.

Another 300 people were murdered over Ireland on an Air India plane, thanks to Canadian security ineptness. Fortunately the Indian murderers were almost as inept as the Canadians: they actually wanted the plane to blow up on the ground at Heathrow.

We don't trust any foreign security. And thousands of travellers owe their lives to that.

We sometimes have to go through security again at Heathrow & Gatwick after arriving from Edinburgh, i.e. another airport in the same country ! Like others have said, it's because unfortunately we sometimes get corralled via the same route as passengers arriving from flights from all over the world.

Having read all the replies, it now makes sense - I hadn't thought of it like that. However, there is one aspect of security (or rather lack of it) which I just cannot understand. A passenger is free to take "duty-free" on board, which might well mean, say, a large bottle or two of spirits, which to me could make a very threatening weapon. A nailfile is not allowed, but breakable glass bottles are? Is that not crazy?

Aren't you also forgetting the *ahem* "unpleasantness", between Britain and Ireland over the last 35 years?

And as Flanneur said - why should we trust any other country? So far we've got a perfect batting average on our own security - why take risks?

It is not crazy (well, it IS) if you keep in mind that many airports generate more revenue from retail and restaurant than from the actual air traffic fees.

I think the OP would not have been so annoyed if security screening had been done is a less time-consuming manner.
It is one thing to add additional security measures, and another thing not being able to handle that business.

irishk - Nail Files are allowed on board.

rkkwan - maybe I picked a bad example, but surely you get my point (forgive the pun!!)

Audere est facere

Your comment doesn't warrant a reply - my only reason for doning so is to make that point!!!!

So the period 1968 to 2002 was just a figment of my imagination?

I'll tell that to the people I knew who were involved. Well I would - but some of them are dead.

IME nail files are not allowed.

Rounded nail files are permitted - but pointed ones IME are not. In fact, my last 2 trips through London airports I observed security officers snapping the pointed nail file off of nail clippers.

The nail clippers were fine but the attached nail files were not.