Nothing showing, with connection to Cornwall, in FreeBMD, nor Ancestry for Sydney Tann. However, there is a death in Cornwall for Thomas Sidney Tann, plus birth and marriage registrations for Thomas S Tann in Cornwall/Devon.
There is a younger man, who appears to be the son of Thomas Sidney Tann, born in 1946. He died in 2006 registered as Michael Thomas Sidney Tann - although the birth index shows Thomas M S Tann. He was married in 1968 in St Austell.
Until the 'no-fault' divorce became law on 1 January 1971, only the 'innocent' partner in a marriage could initiate divorce proceedings - or choose not to do so.