Paperclip,
It appears i'm in the same boat as you!
When I got the email saying contracts out in two weeks i did raise an eyebrow, I chased them up and got a further email last Friday saying it had been posted that day.... mmmm 6 days later and still nothing. I know Royal Mail are a bit suspect but 6 days? mmmmm again!
To the person ref security clearance - think it's generally a maximum of 6 weeks but think it may be a touch longer if you've been living outof the UK.
To the person that is going to buy the books for stage 3, not sure how helpful they will be ? I know things have changed a little bit since I did mine in January, but they wouldn't have helped me. The interview was a competency based interview (try and think of situations you have been in before, what you did, what was the outcome etc) and prior to that it was a group exercise! Damn bus routes!
