Clue: M Antony's friend, one reversing vehicle behind obstruction (9)
Answer: ENOBARBUS
Explanation: Definition: M Antony's friend
A charade of ENO ('one reversing') plus BAR ('obstruction') plus BUS ('vehicle'), for the character in Shakespeare's *Antony and Cleopatra* who was (on and off) 'M Antony's friend', and was based on the historical Gnaeus Domitius Ahenobarbus, one of a host of people with those names, most of whom managed to be elected Roman Consul. I think the form 'M Antony' refers back to another crossword clue, but I cannot put my finger on it. Anyone with a better memory?