Out of all the popular cities in United Kingdom, Belfast is the cheapest city to rent a car in at just $13/day. Renting a car in Belfast is 28% cheaper than renting one in Cardiff where the per day rate is around $18. Other fairly inexpensive cities in United Kingdom to get a rental car in are: Bristol ($13/day), Newcastle upon Tyne ($14/day), and Leeds ($14/day). While these cities typically have cheaper prices than the rest of the country, travelers looking to rent a car in London should expect to spend around $15/day on their transportation. The most popular city to rent a car in United Kingdom is London.