Tesco are a good employer etc. I dont know if your going away or staying at home for uni but tesco do the option of "store clearing" where you move stores to suit you. So during term time your in store X and when your at home your in store Y.
I sent my CV of to several places and got replies from all. Ive now been working for tesco for two years. Most people at uni work one weeknight (usually till 9 or 10) and one day at the weekend, and tesco will be fine with you doing this.
Just basically say you will be starting university and september and providing the hours fit in with your timetable you will be able to work mon, tue thu untill 10 and a saturday. Say you wish to do around 10-15 hours as its a reasonable ammount and there is normally alot of overtime to suplement your wage.
Good luck.