Hi, when I applied to Virgin, I'd had three weeks off sick for surgery and recovery after within the last two months and it didn't stop me from getting invited to interview and then getting the job. I made sure i put on my application that the three weeks were all in one block and supported by doctor's notes.
With regards to your previous employer not being allowed to disclose your sick record I'm really not sure. Just be honest about why, and how long you were off. They understand that people get sick.
Good luck with your application