Bit late, but you probably would’t have got that one. Whenever I’ve hired a car (albeit only a handful of times) I’ve booked the smallest cheapest one on their website and they’ve never actually had one when I’ve collected it. Book a 1.0 matiz/get a 1.4 corsa type thing. Happened even after they did a hard sell for the upgrade. I do wonder how many of the small cars they actually have compared to the bigger types. Still, £20 for not having to hope isn’t so bad.
Next thing for them to sell you is the extra insurance, they’ll point out that otherwise there’s a twelvety billion pound excess if it gets rained on. Enterprise charge something like £20/day for that, although they can be haggled with, and your can get it from other companies. ‘course, hertz might be different.