It's interesting how this stems from a cultural difference. In very general terms, the UK is based on common law, in which we decide the truth as we go, based on the decisions of parliament and court cases. Spain and France are based on civil law, which are much more rigid and top-down, but also more clearly defined. In civil law, if it's not explicitly declared illegal, you can do it. In common law, it's a little murkier. This even seeps into the language (The French say they "have the right" to do something, the English say they are "allowed" - active vs. passive).

Of course there is great overlap between the two in reality, but at their core the two legal systems have different philosophies. Hence why you end up with situations where the UK may be more flexible about things like separation.