Hi been offered a graduate job with a leading consultancy, just have a question with regards to a pre-joining health questions. I used to suffer from occasional mild panic attacks, I have been ok for nearly two years now, but will this affect my job offer negatively. I am concerned they may withdraw the offer.

That's your own concern. I wouldn't declare it. It was a personal matter and no one's business but your own

I completely agree. I suffer from mild panic attacks, but now am more or less in control. I work as a consultant in top stgrategy house, never was an issue. just keep some xanax in the pocket :)