Another great Sunday puzzle.
Set up company on time, and work for influential organisation (7) = OCTOPUS
set up = reverse, company = CO, time = T, work = OPUS
Favourite clues (of many):
Unfriendly resistance put up by school? (11) = STANDOFFISH
Double definition if split 4,2,4
Around area, shows signs of radioactive emissions (4,4) = BETA RAYS
around = containment, area = A, shows signs of = BETRAYS