The entry form says "PLEASE ENSURE THAT YOU HAVE AFFIXED SUFFICIENT POSTAGE TO COVER NEW INCREASED POST OFFICE CHARGES FOR RETURN OF ACCEPTANCE FORMS!!"

But it asks for a 9" by 6" SAE, which is within the 9.45" by 6.5" maximum size covered by normal stamp. So can we assume the package is not more than 100g in weight, or over 5mm thick? If so, a normal stamp will cover it. It was only a thin booklet last year as I remember.