Ever since I've had my car (from new, 2 and a bit years now) the coolant level has remained at the midpoint, right where the join in the tank is. When I checked last week the level had dropped slightly and it was near the min mark. I've just checked again now and it's on if not slightly below the min line. I can't see any signs of leakage on the pipes or tank by looking down into the engine bay, but I'm guessing there is a leak somewhere and it's not just contracting because of the cold. I should probably take it into a garage, but is there anywhere else I can check for possible leaks?

Hopefully it's not in the heater matrix pipes and leaking inside the car or getting round the head gasket!

Cheers

Unscrew the oil filler cap. If coolant is getting in the oil (blown head gasket) then you can often see a white scum on the underside of the cap

Checked the coolant cap is on nice and tight, could be something simple like that.