A tank of unleaded fuel now costs nearly £4 more than it did six months ago, and experts predict the price to rise even further.

Motorists have begun the new year by paying the highest price for petrol since the end of 2014, as the “good times of lower-cost fuel” come to an end.

The average cost of unleaded in December rose for the second month running, from 120.66p to 121.11p – a 0.45p increase – while diesel went up from 123.06p to 123.46p – a rise of 0.4p.

A litre of petrol is now at its highest point since December 2, 2014, whereas diesel owners will be hoping never to see the 147.93p a litre they were charged in April 2012.

Both fuel types have increased substantially from July, when petrol was at its cheapest last year – 114.33p a litre – and diesel was 115.02p. This means a tank of unleaded for an average 55-litre family car now costs £66.61 – £3.73 more than it did in July. For diesel, a fill-up now stands at £67.90 – £4.64 more than last summer.

The current higher pump prices are a far cry from early 2016, when both fuels averaged 102p a litre. But, more positively, they are still considerably cheaper than April 2012, when the UK average prices of petrol and diesel reached record highs of 142p and 148p a litre respectively.

The price hikes have been driven by the increased cost of oil, which is now at its highest since May 2015 at 66.61 US dollars a barrel – the cost rose 3pc last month, having started the month at 64.59 dollars.

RAC fuel spokesman Simon Williams said: “Sadly, December was the month oil reached its highest point for over two and a half years – something which motorists are now feeling the effect of at the pumps.

“On a brighter note, the shutdown of the North Sea Forties pipeline didn’t cause the price of oil to increase as many expected. It had been feared this would lead to petrol and diesel going up in the run-up to Christmas but, luckily for drivers, global oil production wasn’t negatively affected.

“It’s hard to see pump prices getting much cheaper in the early part of 2018. Unfortunately, the good times of lower cost fuel appear to be over and it’s probably now far more likely that we will see them going up as OPEC’s oil production cuts are starting to have the desired effect of reducing the global oil glut and pushing the barrel price higher.”