It will be around 6 PM. In order to be more precise, you will need to specify exactly what day, and precisely where in the UK you mean. Sunset on September 1 in the Faroes will be a LOT different from sunset on 9/30 in Cornwall or London.
The time of sunrise and sunset is very dependent on the precise location and the date in question. Please re-post your question with the date and the city name or ZIP code.
You can calculate the time of sunrise and sunset easily by visiting the United States Naval Observatory web site's Sunrise & Sunset calculator. You will need the date, city and state for US locations, or the date, latitude, longitude and time zone for any other locations in the world.
The site is
http://www.usno.navy.mil/USNO/astronomical-applications/data-services/rs-one-day
You can also calculate the times of sunrise and sunset for one year at a given location at the site:
http://www.usno.navy.mil/USNO/astronomical-applications/data-services/rs-one-year
On September 25, 2011, the sunset time in Duxford, UK, was approximately 6:50 PM local time.
sunset times change constantly. For example on Saturday 15th August 2009 the sun sets at 20:23. The following Saturday the sun sets at 20:08 and so on.
at 6:58 PM BST
18:16
Sunrise: 6:44am Sunset: 7:04pm
at 7:39 PM EDT
18:49 (6:49 pm) EDT
9/10/11 North Myrtle Beach sunset: 7:28 PM EDT
The time of sunset depends on where you are. In New York, for example, sunset on September 3, 2008 will be at 7:25 p.m. In Anchorage, Alaska, however, sunset on the same day will be at 9:01 p.m.
Sunset was 6:47 pm ET on September 27 2008 in New York.
Sunset is 7:29 pm CT.
Sunset at Rawlins on 23 April 2011 was at 7:58 PM Mountain Daylight Saving Time.
The sun is setting somewhere every minute of every day. You need to specify a city or a set of geographical coordinates.
Sunset was at 7:40 PM PDT.
On September 1, 2015, the sunset in St Andrews, Scotland was at approximately 8:03 PM local time.
6:30