[rahimnathwani]

"The roads are free at the point of use, the tube isn't."

No they're not. They are partly funded by general taxation, just like the NHS. However, if you want to drive your car on the road, you can't just drive it. You have to first pay a specific 'vehicle tax' which is per vehicle, per year: https://www.gov.uk/tax-disc

Furthermore, if you want to drive in most of Central London during the day time on a weekday, you have to pay the congestion charge: https://www.tfl.gov.uk/modes/driving/congestion-charge