The average price of petrol reached 167.3p per litre and 179.3p for diesel on Tuesday, according to RAC data.
Fuel duty has been frozen since 2011, and the Chancellor noted this reduction is the biggest ever cut to fuel duty and only the second time it has been cut in 20 years.
Fuel duty on petrol and diesel will be cut by 5p a litre. The change comes into effect from 6pm today.
Fuel duty is currently 57.95p per litre, so this change means it will reduce to 52.95p per litre.
This new level of fuel duty will stay in place for a full year, until March 2023.
The Chancellor says the cost of this change to the government finances is worth more than £5bn.
Individual forecourts set their own prices, so as always you should shop around to find the best deals.
You can expect to see prices drop begin to drop in the coming days as forecourts compete for business following the reduction in tax.
Your bill at the forecourt will depend on how large your car's fuel tank is, and your overall saving on fuel will also depend on how fuel-efficient your car is and how far you drive.
For a typical petrol car with a 55-litre tank and based on yesterday's average fuel price for unleaded, you would have paid £92.02 for a full tank. With the fuel duty cut, the new price you'd expect to pay is £88.72 (fuel duty attracts VAT at 20%, so the overall saving is actually 6p per litre).
This results in a saving of £3.30 to fill up your tank.
Fuel duty is one of the taxes the government places on petrol, diesel and other fuels, used both in vehicles and also for some people heating their homes.
The rate of fuel duty is the same for petrol and diesel, although it does vary for some other fuels. For example, 'fuel oil' burned in a furnace or used for heating is charged at a much lower rate (10.70p per litre).
In addition to fuel duty, you also pay the standard rate VAT at 20% on most fuels including petrol and diesel - this isn't changing with the fuel duty cut announced today. This VAT rate also applies on the fuel duty itself. Domestic heating fuel has a reduced VAT rate of 5%.