It's a matter of protocol. Most people won't think of those details, and that is why the provision was originally included in the bill. I am not the only member to make that suggestion. Chris Charlton proposed a very similar provision, and Inky Mark, a former Conservative member, did the same. The idea was to lower the flag to half-mast. Sorry, I can't remember how to say it in French.
On March 30th, 2015. See this statement in context.