My son worked for Sainsbury's last year. It was terrible. He applied for a job, got an interview for a different job where they told him they would never employ a student in that role! He explained that he'd applied for a different job and that was that. He'd also applied for a similar role at another branch simultaneously where he got an interview. They offered him the job and he got instructions to say he had to go on a training course. When he got there, he wasn't on the list but they trained him anyway! Half way through they came back to him, said that he should have been at another centre but they'd given him the wrong instructions. They gave him the start date for the job and sent him off to join the first store he'd not quite been interviewed at! He turned up on the relevant day, nobody knew who he was but they let him work anyway. They came back to him later to say that they'd been expecting him the following week so, once again, he showed him the email he'd received confirming what he'd been told. They let him stay, he worked his hours and they told him what time they wanted him the following week. He turned up at said time only to be told off for being an hour late. He was gob-smacked.
I have to say they didn't get any better and after 3 months, just as he was going to get his discount which I was really looking forward to, he left. On his last day, having put it in writing for them, he turned up and they said they weren't expecting him to be there...they let him work anyway. The moral of this story, if you want a job, just turn up at Sainsbury's. It seems they will be used to not knowing who there staff are and if they should be there ???