[Tannaton]

Sitting for a week would not bother a healthy car and battery.... sitting for 3 months maybe....

With regard to MOT emission, if it is normally driven gently then an "Italian tune up" will probably sort it, do half a dozen runs from say 20 to 60 with your foot to the floor.

Wife used to have a Kia Ceed and had the same problem, a good thrashing later it was fine. Carbon in the exhaust can get loosened on the fast acceleration run and cause a higher reading on the opacity meter.

Or the garage is trying it on....