I was flying with my wife, and we did a controlled experiment, since the Pre line and regular line both looked daunting. We got on different lines at the same time. We both took about 45 minutes to get through, but the Pre line was actually a bit slower.
I flew last November, from Trondheim (Norway) to Amsterdam, round trip. Both times I had to take my shoes off. But the rest of the screening process is much quicker, and the lines aren't as long. I even got extra searching when I arrived back home and it was quicker than the waits in the US - and that dude went through all of my stuff. I happily travel lightly, but still not bad at all.
Heathrow's FAQ: "Do I need to remove my shoes at security? Only if you’re asked. Some passengers will be asked to remove shoes in order for them to be x-rayed."
Gatwick's FAQ: "You may be asked to remove your shoes and belt before going through the security archway."