The average petrol price rose by 6p a litre – the worst monthly increase since the RAC began collecting data in 2000.

Unleaded shot up to 129.41p, taking the cost of filling up a 55-litre family car to £71.18 – an increase of £3.29 in just one month.

RAC fuel spokesman, Simon Williams, said: “May was a hellish month for motorists. Sadly, they have been besieged by pump price rises for three months with nearly 9p a litre being added to petrol since the beginning of March.

“The rising oil price together with a weaker pound is a punitive combination for anyone who drives regularly.”

The RAC Fuel Watch data showed the average prices of both petrol and diesel have gone up every single day since 22 April, adding 8p a litre in the process – the longest sustained price increase since March 2015.

However, Williams said the oil price “cooled a little” to $76 a barrel in the last week of May and the RAC’s two-week forecast is currently showing that average prices may “even reduce by a penny or so”.

He added: “Looking at the bigger picture, there is talk that OPEC – the Organization of the Petroleum Exporting Countries – may agree at its meeting on 22 June in Vienna to change its tack of restricting oil supply.

“The group, together with Russia, have been limiting production with a view to removing the long-term oil glut. This strategy has been successful and, as intended, caused the barrel price to rise. If a decision is taken to increase supply it may provide some much-needed relief for motorists at the pumps in the UK.”