Complex sentence: Most travellers are unaffected, but HM Customs have the authority to stop and search suspected transgressors, with reported draconian instances of cars and contents being confiscated on the spot.
Split into simpler sentences: Most travellers are unaffected, but HM Customs have the authority to stop and search if they suspect transgressors. They can be draconian: there are cases of cars and contents being confiscated on the spot.