hey thats also my start date!
these things can happen, and i don't know, and don't know if anyone knows what the magic requirements for the assessments but, one thing i did notice if you see any Lighting Panel Operator jobs going (Heathrow or Gatwick only i think) then when i applied i had to sit the ATCO stage 1 assessments before interview, so even if you don't have the intention of doing that you could always apply with the chance you get more practice at it!
good luck, i failed my first attempt at the stage one assessment, recently passed the stage three so its anyone's game!