This must be the simplest Times Jumbo Cryptic ever ... what usually provides a few days' enjoyment took me just over an hour! BUT ... 10a - OGPU? Can't find any reference in dictionaries or on google that take you to this. Secret police .... ? And where does "up go" come into it (..."on horseback" presumably?) Since almost all the other clues in this one were so easy and basic, I'm sure I must be being being thick - but can someone elucidate for me please?