The longest note held in a UK Top 40 hit.
The longest note known to of been held on a UK chart hit belongs to a-ha‘s Morton Harket on their 2000 single “Summer Moved On”. It lasts for 20.2 seconds.
Runner up is, hardly surprising, Bill Withers for the long “daaaaaaaaaaay”, sung in ‘E’, on his 1978/88 hit “Lovely Day”, which lasts for 18.1 seconds.
Third place is Donna Summer, who made it to 16 seconds on her 1979 hit “Dim All The Lights”.