Foreign Office certain about government leader being detained by undesirable elements (8)
I believe the answer is:
fogbound
'detained by undesirable elements' is the definition.
(trapped in fog, type of weather or 'the elements')
'foreign office certain about government leader' is the wordplay.
'foreign office' becomes 'FO' (abbreviation).
'certain' becomes 'bound' (as in the phrase 'it's bound to be').
'about' means one lot of letters go next to another.
'leader' suggests taking the first letters.
The first letter of 'government' is 'g'.
'bound' after 'g' is 'gbound'.
'fo'+'gbound'='FOGBOUND'
'being' acts as a link.
(Other definitions for fogbound that I've seen before include "Enveloped in thick one ac" , "unusable as airport -- ?" , "Enveloped in thick mist" , "hidden in pea soup?" .)