I think various posters are stating that you should be prepared for the possibility because rules and implementation differ by location. Even if the rules do not require it, security officers have a range of discretion. If you cannot do this by yourself it would seem prudent to choose a different case to use when flying.
That makes sense and I will look around for a case that I can handle in this situation. However, I don't have any plans to fly to LHR anytime soon.