Very easy to distinguish if something is a jet. All aircraft will have flashing lights. The ISS is not only visible with the naked eye, it is the brightest object in the sky and very easy to view. This Sunday is a real good viewing time as the ISS will be pretty high above the horizon(65 degrees with 90 being straight overhead. It is also a pretty long view of 4 minutes. Also Friday the 13th has a great one. Here is one link to check out upcoming viewing. NASA is usually my go to. This one has Manchester plugged in for me.
https://spotthestation.nasa.gov/sigh...r#.Wd-Bluk5CUk