It's not allowed in the Netherlands and Belgium. I thought it also wasn't allowed in the other european countries but I'm not a 100% sure about that.

If the police are allowed to lie about evidence then this undermines the suspects chances for a fair trial (false confession). If the defense can show at a trial that the police lied during the interrogation, this would impact the chance for a conviction. At least this is how it works in the EU. In the US, I have the impression the judges don't take this into account.