The police have a number of methods they can use to investigate grow houses in the UK. One common method is using infrared thermal imaging cameras to detect heat signatures from the homes. This can be done from a distance and can help the police to identify which homes are being used to grow cannabis. Another method the police may use is undercover surveillance. This involves sending officers to pose as members of the public in order to gather information about the home and its occupants. This can be a risky method of investigation, as it relies on the officer being able to blend in and not be detected. If the police have reasonable grounds to believe that a grow house is being operated at a particular address, they will obtain a search warrant from a magistrate.