The fuel consumption of the Ford Focus we hired was staggeringly good (after a Rangie!) - 52mpg or 5.4 litres/100km on petrol.


Yes, we were getting 1000km out of a tank of diesel in our Focus when we were there.
We went in the off season when the B and Bs were happy to bargain just to get someone in overnight, so that helped with our accommodation (plus my wife and DIL love to bargain).
In London we didn't drive, just walked or caught buses or trains and an occasional taxi.
Sounds like it was definitely quieter in London in the offseason when we were there than what you found.
The part of our trip I enjoyed the most was using the Focus to pull into quiet villages and wander about. Pub lunches and cafes were quite reasonable. I didn't have a beer, although I did sample the Scottish whisky (and bring some home).
When we were there houses prices outside the major city centres were quite reasonable by Aussie standards. We could buy there and not have a mortgage. Have you noticed that?
There are some excellent bookshops in London.