Istanbul doesn't observe daylight saving time but Cheltenham does. DST in Cheltenham started on 31 March 2019 and will end on 27 October 2019. Once DST ends in Cheltenham the time difference between Istanbul and Cheltenham will be -3:0 hours.
Time zone: TRT - Turkey Time (UTC/GMT +3)Time zone difference / Flight distance
Time zone: BST - British Summer Time (UTC/GMT +1)DST started on 31 March 2019DST will end on 27 October 2019Time zone difference / Flight distance