I have a 1.8 T27 Avensis estate, and I am currently averaging over 37 mpg. The worst average I have seen is 33 mpg. The car can go 370 miles with at least a couple of bars on the fuel gauge, depending on driving style. I know that my car has 60 litres (13.2 gallons) fuel tank compared to the 50 litres 11 gallons) on the Auris. I fill up from 35 to 47 litres depending how much fuel remains. I do occasional short journeys (uphill to my mum) some journeys across London around the South Circular, local journeys in my borough of Bexley which don't have many 20 mph roads or speed bumps compared to other borough like Greenwich or worse Lewisham, which has a blanket 20 mph on every road it controls.
I have the tyres pumped to 36 psi which helps, and change up early when possible. The rust of brakes should rub off, depending on how severe the rust is. Hopefully the brakes are not binding. If you live in one of the out London Boroughs near a dual carriageway, go for a drive and lightly press the brakes to clean the discs. If that doesn't work, it will be a new discs and pads.
I would be disappointed if I couldn't match my current car consumption, if I had your car.