Unfortunatley I think you have two choices. Either carry on with the biscuit for an easy life, or its going to take a week or so of dealing with a screaming child to get him back out of the habit! I did exactly the same as you with my daughter, bribing with food for everything! I ended up starting a sticker chart, and her challenge was to climb into her car seat by herself. Then if she managed it she got a sticker to wear to nursery and show her teacher how grown up she has been. Then when she did a whole week she got a sun lolly (no calories or additives-clever )Worked a treat at 2 1/2. Maybe try that?