You're not going to find a much more efficient car than your Corsa, unless you consider diesels. A cheap, second-hand diesel can be very expensive to maintain, though - especially as you don't cover many motorway miles (which are necessary to clear out the diesel particulate filter and prevent issues). Before you go trading in your Corsa, have you done everything you can to ensure it's as efficient as possible? Consider clearing out any unnecessary items and have it serviced. If you still want to change your car, we'd recommend something like a Hyundai i20, Honda Jazz, Toyota Yaris or Ford Fiesta (with the reliable 1.25-litre engine). They're all very efficient and should be very reliable.