Currently standing at £11.50, Johnson has said that the next mayor will have to increase this or introduce "smart charging" at peak times, especially if they want to introduce schemes such as pedestrianising Oxford Street.
Luckily for the next mayor, most Londoners are prepared to pay up to £15 a day if the money is spent on walking and cycle schemes, public transport and improving air quality.
Some 42 per cent of Londoners would actively support the increase in congestion charge to £15, compared with 30 per cent of Londoners who are opposed to the increase.
"With traffic delays worsening, London’s population increasing and road space under growing pressure, mayoral candidates need to show how they would reduce the gridlock and clean up London’s air. London’s air quality situation is critical – I feel it every day on my bike journey to work," said Kevin Craig, managing director of PLMR, which commissioned the polling.
He added: "Whilst both Sadiq Khan and Zac Goldsmith have refused to commit to an increase in the congestion charge, our polling shows Londoners are willing to pay more to ease traffic in the capital and invest in walking and cycle schemes, public transport and London’s air quality."
The issue of congestion has become politically charged recently. Londoners recognise the problem only too well. In a recent ComRes poll for London First, 63 per cent of Londoners said they thought congestion had increased over the past two years, while some 75 per cent thought London will be more congested by 2020.
London First's David Lean said that the city needs to revisit the congestion charge – and reconfigure it for the challenges of today. Instead of a blunt lump payment, London needs to move towards a geographically broader and more sophisticated charging system, with charges varying according to those roads and times of day where congestion is worst.
Interestingly, Conservative voters were more in favour of the fee increase than Labour voters.
Some 48 per cent of those who voted Conservative in 2015 supportive, compared to 45 per cent amongst Labour voters.
However, Conservatives are also the most polarised political party with 32 per cent opposed to the change.
UK Independence Party voters were found to be the most opposed to an increase whilst Green voters were the most supportive.
Male Londoners were also found to be more strongly in favour of increasing the congestion charge than women – with support ratings of 46 per cent and 39 per cent respectively.