Filling a large family car with a 70-litre tank — such as a Ford Mondeo — with unleaded petrol now costs £98, a rise of £6 since the start of the year. A diesel family car now costs £103 to fill, £5 more than at the start of the year. Experts say the cost of unleaded petrol is likely to spiral towards 150p a litre by the end of the summer, particularly as George Osborne refused to cancel the proposed August fuel duty rise in the Budget this week.