No Northwing, civil twilight is when the sun is between 0 and 6 degrees, whether it is rising or setting. As far as the Rules of the Air are concerned, the twilight hours are considered to be daylight as the CAA do not have any 'twilight' regulations. So therefore, in answer to 3142's question, it is possible to fly a day VFR flight during civil twilight.
Airclues