For some reason, A&E decided not to air the episodes from season 4 of Spooks (MI-5) after late January. I can only guess that bad ratings is one of the reasons for A&E to dump the show in favor of more watched fare, like Rollergirls, Dog Bounty Hunter, Growing Up Gotti, etc.
BBC will be airing season 5 of Spooks later in the fall this year.