I called Environ as I saw a mouse and had used the company in the past. They did not fill in any holes (the procedure has changed since my last visit), but delighted in showing me (a girl who is petrified of mice and lives alone), all of the holes that a mouse could come through that they were not going to fill. The guy also said that he could hear mice in the ceiling in the bathroom with a loud extractor fan on (I can't hear anything but the fan). I essentially paid £166 for someone to come over put down a bit of poison and leave me in tears (fearing all the mice that could enter my flat)...I will need to pay more if I want the many holes filled :-(