Apple Airport Extreme's - causing packet loss on network - why?

Unless they were subjected to some external force such as a lightening strike or some surge while they were at the client's home, it's highly unlikely that they would both exhibit this behavior.

I'd first make sure that they have the latest firmware. Second, were they exhibiting this behavior before moving them to your environment?  If so and if upgrading the firmware doesn't fix the problem, then I would suspect that they were hit by some external force while in the client's home and the hardware made be damaged.

As a check on the above, take them to some other environment and set them up, one at a time and test.  If the problem follows the device then it's most likely that the device has a problem.

I took them from the clients place as they had not successfully set them up. I reset them and upgraded them and set them up from scratch.
This morning I've had one of them on and about 1 in every 100 pings we get a request time out.
I don't think we get any when we don't have them attached.
They may have been purchased originally in the US and are now being used in the UK.

I don't think they would have been struck by lighting. I think it's likely to be a network or setup issue of some kind, just trying to work out where to start looking.

I'm now going to put other one on and see if we see the same increate in ping drops as we did yesterday.

Does the ping drop rate increase the longer they are on?  It's also possible that you have some interference in your office that may be affecting the wireless connection. If the other one does the same, I'd still take it to another environment, perhaps one with less potential interference than may be in your office and try it again. Assuming that no electrical damage has happened, it's highly unlikely that two APE's would exhibit the same issue...it almost has to be environmental interference like some other wireless device or perhaps even something in the outlet they are plugged into.

Further investigation has revealed that when I just have the main airport extreme on, I have very few issues, get the odd time out, but not many

when I have them both on, there is a lot more.

But the current challenge is that I Cannot set them to be for the UK.
Looking at the wireless settings it gives me various South American countries as choices, but I cannot select UK as a company of operation.
(that is where we are)
Does anyone know a way around this, or is it simply going to be that an American version of this product cannot work in Europe?

From what I can tell, the wireless settings are regionalized, to meet the differences in different parts of the world. I suspect that if you bought a AE from somewhere in the UK it would be set appropriately.  Having said that, I would assume that if your laptop or whatever device you are using operates on a WiFi standard that the AE you have supports and on the channels you have listed, it should work.  If your wireless device has settings that are not supported on the AE you have, you may need to turn them off, but honestly that's mostly a guess. I think as you change country settings different options probably appear or disappear.

The issue I have however, is that there is no option to select UK in the options.
I spoke to Apple support but they are having phone issues today and are planning on calling me back.

Solved with Apple support mainly.