I haven't seen a thread on this possibility and I'm not convinced it would have made much difference anyway but here goes.
What would the effect on the war have been if Germany had mounted sabotage attacks in the UK against say the rail network? I'm envisioning small squads of about a dozen men each dropped by parachute or landed on the coast, well supplied with weapons and explosives.
I'm sure they wouldn't last very long or even achieve a great deal in physical terms but the impact on morale at home might have been significant if they took out a few bridges and perhaps some Home Guard units, especially if fresh teams kept being inserted.