Your mileage qualifies you for a diesel but, though it won't be EU6 for this money, there's no avoiding a DPF and its potential failure and cost. 20,000 miles a year means a new timing belt and waterpump every three years for anything with a timing belt: a £500 expense on Fords and anything VAG. If you can find a Renault Megane with the chain cam 1.6DCI 130 engine within budget, that might be a contender because to offers the latest diesel technology and, over the past five years, has been reliable.