Originally Posted by anabolism

In my experience, LHR security is the most aggressive in the world at sending bags for secondary screening for anything that looks at all unusual to the X-ray person. My advice is to look at everything you bring to see if anything might possibly seem dense or electronic or potentially sharp or liquidy. For example, packages of wipes (surface, baby, hand, butt), electric razors, electric toothbrushes, charging adapters, battery packs, empty bottles, nail clippers. Put everything like that in a plastic zippy bag, as large as needed (e.g., gallon or 2.5 gallon), and when you get to the security belt, take that bag out along with your liquids bag and all electronic devices larger than a cell phone (laptops, tablets, readers, video players), and put all this in bins. If the belt person asks you what the large bag is, explain that it does not contain liquids but has everything that might look unusual on an X-ray.

In my experience, having anything unusual or electronicy or liquidy or potentially sharp in your bag can cause that bag to get marked for secondary, which is usually a time-consuming and unpleasant process at LHR. There is often a lengthly wait for secondary inspection agents to get to your bag due to the large number of bags being so selected, and depending on the agents and what the issue is, your bag may be slowly and meticulously unpacked, with an agent pawing each and every item (one even stuck her (gloved) fingers into each a boxed piece of chocolate handed out on my flight just before landing), often sending many of them for additional X-ray checks as well. In my own experience, it is well avoided.

Of course, YMMV, and I have had bags zip through LHR security unmolested even with liquids left inside, but far too many times I had bags sent to secondary because of something minor that the X-ray person didn't like the looks of.