Thanks for the feedback. To clear things up: I live in Germany, not the UK, and I'm talking about US MPG. In Germany, we have a different system of measuring fuel efficiency - we do liters per 100 kilometers instead of miles per gallon (which makes sense, given that we use neither miles nor gallons). The mileage is that low because the car belonged to an older woman who is now in her 90s and hasn't really driven it that much for the past 20 years, only short city trips to the supermarket or to visit friends and relatives. Due to her condition she can't drive anymore and her son in law wanted to get rid of the car and made me that irresistible 50€ offer.
The condition is pretty decent, at least from a technical point of view. In terms of aesthetics the car is a bit of a downer but I've seen worse on younger cars so it's not too bad. The engine sounds normal, no leakage or other (visible) mishaps.