I was busted in the UK in a similar fashion, but the CID guy said that he was entering my property under the suspicion of smelling MJ. Now believe it or not, the UK is classed as being in Europe, although as the OP (original poster) said, it uses the GBP/£, not the EURO/€. Now I lived in Scotland which also has different laws from England, even though it is in the UK, but I woudl say in your case a fairly similar set of laws. Even if you say the police didn't have a warrant, they will say they could smell drugs and entered the property on that basis. Have you been charged with cultivation? What exactly are your charges? Sounds to me like a half arsed job, the feds took absolutely everything related to growing when I got nabbed. Get a lawyer, plead guilty to possession and you'll probably get a fine, or a caution if you don't have previous. Unless someone is snitching on you they have no proof of Supply.
Good luck,
DST