Jetsetter5... If you have a local security pass for Gatwick and work airside just telephone ATC and tell them the story. If you work for the airport authority they'll probably let you up there anyway.
So many people come on here asking how to visit a tower - and it is difficult nowadays with increased security - but they could save themselves a lot of time by picking up the phone! As someone once said in a similar thread - it demonstrates initiative.
Good luck with the tests, etc.