The cost of filling up at the pumps has edged up over the last month, with diesel drivers getting a worse deal than those using petrol, according to figures from the AA.

The average price of petrol in the UK has risen from 133.35p a litre in mid-May to 134.61p in mid-June, while diesel has gone up from 138.17p a litre to 139.16p.

Northern Ireland has the most expensive petrol, at an average of 135.8p a litre, with London having the cheapest, at 134.61p.

Northern Ireland also has the dearest diesel (139.8p a litre) with London and south west England having the least expensive (139.1p).

The AA said the slight rise in average petrol prices nationally represented "something of a lull" after the 8-10p swings in prices over the last 12 months.

But it warned that this year retailers have on average been "creaming up to £1 a tank extra off diesel car drivers and up to £1.40 a tank extra off diesel van owners".

The AA went on: "At present, the 1p-a-litre premium that fuel stations are generally adding to the cost of diesel adds 5,500 miles to the break-even point for a new car buyer who chooses diesel instead of petrol. Diesel cars typically cost £1,500 more but the saving from better fuel efficiency should eventually recoup that."

AA president Edmund King said: "To be fair, there is often much greater variation in the price of diesel among retailers in a town than with petrol. However, on average, the profit margin on diesel is consistently at least a penny higher than with petrol.

"The clear message to diesel drivers is to take advantage of the greater range of prices locally. Some forecourts are more diesel-friendly than others."