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