Labour’s fuel duty increase will add £156 a year to family bills, according to analysis by the Conservatives.

The prime minister is planning to increase fuel duty by 5p a litre in stages from September.

But his Government has been criticised for refusing to rule out the rise even as fuel prices have surged since the war in Iran broke out.

For a petrol car travelling 7,400 miles per year, the annual amount of fuel duty payable will rise from around £495 today to £573 in three years, the Tories said.

It means the average petrol car driver will be hit with an extra £78 a year by March 2029 while a typical family with two petrol cars will incur an extra £156.

Since the US-Israel attack on the Middle Eastern state the Strait of Hormuz – the narrow waterway through which 20 per cent of the world’s oil and gas exports travel – has effectively been shut down.

Petrol prices have now reached an 18-month high.

Sir Keir told MPs this week he would ‘keep the situation under review in light of what is happening in Iran’ but would not commit to extending the 5p fuel duty discount beyond September.

Keir Starmer has refused to commit to extending the fuel duty freeze beyond the summer

Chancellor Rachel Reeves extended the 5p fuel duty cut from this month until the end of August in last year’s Budget

Shadow Transport Secretary Richard Holden told The Sun: ‘Labour are about to wallop drivers with the first fuel duty hike in nearly 15 years just as families are already struggling with rising costs.

‘Labour are forcing drivers to pay for their economic incompetence.’

But a Treasury spokesman told the paper: ‘We do not recognise these calculations.

‘The Chancellor has written to the Competitions and Markets Authority and met with retailers and energy suppliers with a clear message that drivers must get a fair deal at the pump.’

Chancellor Rachel Reeves extended the fuel duty cut from this month until the end of August during last year’s Budget.

Last week the Mail reported that the Cabinet appeared to be at odds on whether to keep the freeze in place, leaving drivers at risk of a further price shock.

Meanwhile the Telegraph reported Asda has raised petrol prices faster than any other major retailer since violence broke out in the Middle East.

The supermarket hiked its petrol prices by an average of 10.1p to 138.91p a litre since the conflict began, adding £5.56 to the cost of filling a typical 55-litre tank.

Asda’s increase was almost 1p a litre more than the next biggest jump among major retailers.

The supermarket has also raised diesel prices at the fastest rate over the last fortnight, hiking the fuel by an average of 19.86p a litre to 157.52p, adding £10.90 to the cost of filling a typical family car.

War in Iran has effectively closed the Strait of Hormuz. Pictured: tankers sail in the Gulf near the conflict-addled Strait

Earlier the RAC said diesel had risen 16p and petrol 7p on average since the start of the war.

Using the Daily Mail’s exclusive real-time price map, motorists can track the cheapest fill-up near them.

It uses live data from 15 major fuel companies, including Tesco, Asda, Sainsbury’s and BP.

Research from when the tool went live last year found the average driver could save £10 a fill-up, or nearly £200 a year, by switching to a station that is 20p cheaper per litre – the difference between the cheapest and most expensive pumps in one area.

Last week Darren Jones, Chief Secretary to the Prime Minister, said the Government was ‘in a position to do what it can to help’ with rising oil prices.

He told the BBC’s Today programme: ‘The Chancellor has already frozen fuel duty from the last Budget through to the end of this year (sic).

‘Chancellors now have on an annual basis at budget time considered those issues and I know the Chancellor will be looking at that when we get to that point later in the year.’

But the Mail on Sunday reported Labour MPs feared Ms Reeves was ‘running out of options’ to prevent the economy from falling into recession.

Economic experts have warned that if the chancellor tries to help struggling households with taxpayer handouts, she risks breaching her own fiscal rules and making the cost of loan repayments more expensive for the Government.