A reference to Mark Kermode's communist leanings in his youth (and possibly beyond). Trot being a contraction of Trotskyist. As it turns out communism didn't prove to be a great success, but don't tell Mark.
During the Sport Relief Top 10 held at Eton, Simon asked Mark what his younger, Communist self would have made of him being in the cradle of so much of the British aristocracy. Mark replied that he would have assumed it was entryist insurgency mission to destroy capitalism from within. Either that, or he'd just sold out.