When Jeremy mentioned the countdown to the service on the Merc in episode one, and wondered what would happen if he went past the date it said the service was due, James said, "Cooler... Three veeks." It's probably a reference to something like
The Great Escape*, where Steve McQueen was the 'Cooler King' because he was always being sent to solitary confinement - the 'cooler'.
Jeremy's comment this week was carrying on from that
*because The Great Escape seems to be on British TV at least twice a year, so most of us of a certain age have seen it about a million times...