Five year old diesels are bad buys because, while they can be cheap to run for the first few years under warranty, they are expensive once they surpass 60,000 miles. More often than not, they'll need a new clutch and DMF, a new or cleaned DPF, a new turbo, a new EGR.

You can buy a £5000 diesel and have to spend £5000 on it. If you're buying a car with good residuals, you are paying the good residual, you are not benefiting from it unless that car is spectacularly reliable and Audis and BMWs aren't. Mercedes can be okay. Better to get the most for your money with a Ford Fiesta or, bigger, a Toyota Avensis or Lexus IS 250 auto.