As of the last reporting I saw yesterday, UK authorities still have no clear account of the motives or identity of the people they arrested earlier this week outside of the Fairfold air base. They released the suspects surprisingly quickly, however, which tends to suggest no one actually thinks they were linked to a violent terrorist plot.
According to the Wall Street Journal, one emerging theory among the locals holds that "the men, all from London, may have been in the area to steal fuel[.]"