Two useless secret agents are assigned the task of going undercover in Northern England in order to uncover the details of a disastrous terrorist plot being developed in a garden centre.

“Useless” seems harsh and an exaggeration. I would consider a different adjective. I don’t find this logline enticing. Maybe on your next attempt, be more specific. What separates your spy/comedy (I’m assuming) from others? You don’t need to specify the country this is set in. “Assigned the task” is redundant. Instead, put: assigned to go undercover, or simply, go undercover.