Out of all the popular cities in United Kingdom, London is the cheapest city to rent a car in at just $18/day. Renting a car in London is 58% cheaper than renting one in Southampton where the per day rate is around $40. Other fairly inexpensive cities in United Kingdom to get a rental car in are: Glasgow ($18/day), Newcastle upon Tyne ($20/day), and Bristol ($21/day). While these cities typically have cheaper prices than the rest of the country, travellers looking to rent a car in London should expect to spend around $18/day on their transportation. The most popular city to rent a car in United Kingdom is London.