Motorists are pumping out more money on fuel as unleaded petrol prices start crashing through the £1 a litre barrier.

The price of unleaded petrol in at least five of Oxfordshire's 70 petrol stations has risen above £1 a litre. The average price in the county was yesterday listed at 99.3 pence a litre.

In Oxford, the most expensive was at the BP station in Botley where motorists were being charged 101.9 pence for a litre of unleaded. The highest was believed to be 102.9p at the BP in Thame Road, Stadhampton.

The price rises have meant families are paying at least £20 more a month in fuel than at the start of the year, according to the AA.

Last summer, hauliers threatened to block ports and major motorways when petrol prices rose above 96p a litre, but experts now predict that £1 a litre could soon become the norm.

Ruth Bridger, of the AA Motoring Trust, said: "With Middle East crisis, hurricane season potentially hitting oil refineries in the United States and demand steadily going up from China and in other places around the world, it is inevitable that we will get to an average of £1 a litre soon and I think it will probably be this year.

"We will certainly see £1 a litre very shortly for diesel."

The petrol price rise has affected both businesses and individuals dependent on petrol to fuel their vehicles.

Oxford-based driving instructor Roger Coenen, right, said: "These high petrol prices are obviously making a big difference to me, because I am constantly on the road.

"I try to absorb as much of the cost as possible, but if it keeps going up, eventually I have to pass it on to those paying for lessons."

Val Clarke, of the Oxfordshire Driving Instructors Association, said the price increase meant she expected to fork out an extra £500 on petrol this financial year.

She said: "Learner drivers don't realise how much petrol costs.

"Most of them are young and I think it is quite a shock when they find out."

The average price of diesel fuel has now broken through the £1 a litre barrier in Oxfordshire.

TNT spends about £1m a year keeping its diesel-fuelled lorries in Milton Park, Didcot, on the road.

Director of operations Nigel Barton said the increase in fuel costs had had a direct impact on the economy.

He said: "Each day, we have to work out what the customer will be charged, based on the cost of the fuel.

"As the country's biggest business to business supplier, it is worrying if our wheels are not turning because that means the wheels of business are not turning."

Oxfordshire Chamber of Commerce spokesman Kate Norris added: "It is outrageous that unleaded petrol prices have now exceeded the £1 threshold.

"This puts enormous pressure on the many Oxfordshire businesses which rely upon road transport as a primary means to get to work."

Mark McArthur-Christie, chairman of the Oxfordshire branch of the Institute of Advanced Motorists, said: "It is wrong that the Government place a duty on fuel and add VAT to the whole lot."