I understand if you travelling in or to the US, you can lock your luggage using the TSA Luggage Lock. (Immigration is still able to open your luggage using their own special keys)
How about Europe? Especially Heathrow + Charles de Gaulle?
If the TSA Lock is not acceptable in Europe, are there any other alternative precautions I could use instead?
(FYI, information about the TSA Lugguage Locks)