Possible Clues:

• Bet one's not started leisurely walk
• Bet this couldn't follow G, but there's no hurry about it (5)
• Fit enough to encompass mile walk
• Walk miles to keep fit? On the contrary
• Gee! Bet that would make this go slow
• Can get about a thousand without having to hurry
• Walk along slowly
• Blame crash for move
• Execute bet - go easy!
• Gee! Bet you won't be in a hurry with this