If travelling to america from heathrow. do you have to have a lock on your case?

Question

wether it be for insurance reasons..

Answer 1

It would be a good idea.  The case may accidently open or someone could steal from your case.  

Answer 2

Not sure about Heathrow to U.S., but for the return trip, you cannot lock it.  Homeland security visually inspect luggage, so if you have a lock, they may not put it on the plane, or at least delay it.