Click on the link "ISS tracker" on Blue-Grey, and you'll immediately get a live tracker of both orbits on screen - letting you know when you can expect to see them over any part of the world.
I should point out here that to have any real success, and see them at their brightest (and they can be VERY bright), one needs to view them just after the sun has gone down, or just before it comes up, so there is enough sunlight around the other side of the globe, to light them up (reflect off them) in YOUR part of the night sky.
Both are travelling at about 17,300 mph, and the ISS takes about 91 minutes to orbit the world.
When you time it correctly, they DO appear VERY bright, obviously not planes, and do not blink (like planes).
The shuttle looks to be travelling much faster (it fairly races across the sky) as IT is flying at an altitude of about 230km, whereas the larger ISS is orbiting at about 340km up.
They are both travelling WEST - EAST over Britain - a good way of telling them apart from other satellites...
I managed to grab two hasty photographs of them just after the sun had gone down here.
The first I took at 17:57, facing due east, with the camera set to an eight second exposure. I apologise about this photograph - I had no time to set up a tripod, so I was holding the camera on the fence! The star to the extreme right of the first photograph is "Procyon" in "Canis Minor" (just above the neighbours roof), and the star above the trail is "Pollux" (NO jokes here please!) in "Gemini".
The trail of light is an eight second trail of light left by the ISS as it travelled due east.
The second I took approximately 25 minutes later, at 18:20, again with the camera pointing pretty well due east. This time I had a chance to set up a tripod, and could zoom in a little more. The darker (second) photo shows an eight second trail of light left by the Shuttle Atlantis, on ITS orbit west to east. By the way, the two stars in that photo are Castor and Pollux, the twins of Gemini.
It really is worth checking that ISS tracker link occasionally, around dusk especially.
These things are worth seeing (well, in my opinion, anyway).
Its not all about wildlife you know...
NB. Anna and I watched a spectuclar view of the ISS snd shuttle (docked together) traverse the night sky at around 18:20 on the saturday evening after the report above. The light was so bright, I assumed the Shuttle had docked with the ISS, and when I checked the NASA (amongst others) site, I found that it had, early on Saturday morning. I can't imagine how we'd ever get a better view of the ISS - perfectly clear skies, hitched up with the shuttle (so considerably bigger than normal) - it was incredibly bright...