We returned from the UK 10 days ago and rented a Hertz car through Kemwel (a consolidator). They had one of the lowest rates and were transparent to what charges were included and what was not. For a nine day rental, it was $236.00 plus the 50 GBP charge or a one way drop fee. Since the manual was $200 more than the automatic, we chose manual. My husband thinks the hardest part about driving on the left was the left -side stick shift. He was actually amazed that he never stalled the car when stopping at one of the many roundabouts. When we picked up the car from Hertz, they were not pushy about anything-insurance, upgrade, GPS, etc. We declined insurance and said we brought our own GPS. When we dropped the car off in Sheffield, while the car was very dirty, they didn't care and just checked the mileage. I don't even think he walked around the car to inspect. We expected to walk the 3 blocks to the train station, but the agent told us to keep luggage in the car and he'd drop us off. Regarding gas, we paid for a full tank as we knew we'd be driving about 800 miles (about 70 GBP @ 1.27/L), and put in another 65 GBP enroute.
We've used AutoEurope (Eurocar) and Kemwel (Hertz) previously with no issues.