Tesco have a contractor to grit the car park, only snag is they seem to of gone missing in action! its part of the duty manager check, so they are supposed to grit the car park, the backup plan is that the store manually grit the car park but some stores may not of ordered the grit.
Worth a complaint to the Duty Manager, or better still every store has a txt number you can leave a comment, this goes to Head Office and the Store Manager! they have to take action on all negative points if its feasable.
The txt number is on the Every Comment Helps leaflet.