I have done the gatwick one which has changed somewhat and got easier
There is no set order basically you all arrive then get herded into a changing room to put a white bathrobe on. Then you all get grabed by a nurse and led round the stations in no particular order.
Don't worry about it they don't do anything nasty to you. Take a bottle of shower gel with you so you can was all the gunk out of your hair after the flashy light test.
goodluck
MJ