For which tours are organised? (8)
I believe the answer is:
eurostar
'for' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'tours are organised?' is the wordplay.
'organised?' indicates anagramming the letters (I've seen 'organising' mean this).
'tours'+'are'='toursare'
'toursare' anagrammed gives 'EUROSTAR'.
'which' acts as a link.
(Other definitions for eurostar that I've seen before include "Waterloo to Paris train" , "High-speed rail link between the UK and France" , "The train from England to France" , "Chunnel service" , "Channel link" .)