On the Motorway.
On the M1.
On one of the busiest junctions on the M1 (where the M25 joins).
At rush hour.
Somehow, a plastic rod holding the gearbox in place snapped causing me to lose 5th gear. Nursed the car home and (foolishly, I admit) drove to work again today. It managed the journey, but by the time I got there I only had two gears (3rd and 4th I think, as they were where 1st and 2nd should be). Luckily, Kwik Fit agreed to look at it and fixed it quickly.
It's being serviced next week, so hopefully that'll be the end of all this.