Ive been in current for 18 months and im looking for something else and have found some jobs at a tesco store near to me, im unsure as to what reason i can put down as a reason for leaving my current job, could i say something like "i miss helping colleagues and customers" or would another answer be suitable.
No don't be negative about your current job, just let them know you feel you are going to a company at the cutting edge of the modern retail interface and you feel you will be able to challenge yourself more,
What not clear here is are you asking about a reason to give to your current employers? (you don't need to give them one) or a reason to give to your prospective employer?
Usual get-out is to say that present job is not stretching you enough and you want more challenges. Every employer will have heard it before but if you can't think of anything else.
Agree about not being negative about current employer; nobody wants to employ a moaner.