Most roads are actually funded from local taxes - mainly council tax and business rates in any case, not even central funding.
It's not really relevant to my point which is that taxes being collected by consumers of fossil fuels in the UK are certainly NOT being sent to foreign countries to pay for the externalities of pumping CO2 in the air.
As a consumer of petrol in the UK, it's a mistake to think "I'm paying loads of petrol tax, so I'm paying for the externalities" when the money is being spent, one way or another in the UK. While the externalities are global.
1. The UK just hasn't priced it high enough.
2. If the UK does not spend the money raised on ameliorating the externality worldwide, then they have not cancelled out the externality as they might claim to have.
https://www.gov.uk/government/publications/roads-funding-inf...
So central government commits very heavy funding to road building and maintenance such as through the Major Road Fund, but also many maintenance schemes at different levels.
Some local governments choose to forego some of this funding in return for receiving retained business rates instead. However retained business rates is collected by central government and considered central funding.
Ultimately money is a fungible commodity. It is true there’s no direct relationship between road taxes and road maintenance, but whatever petrol taxes pay for would still need to be paid for somehow if they went away.