A family of three, 10 days, driving from London to Oxford, Birmingham, Liverpool, and Manchester. Hotel and London Pass fees have been paid. Planning to buy an Oyster card at the airport and bringing three international credit cards. How much cash is appropriate to bring ?

300 pounds Mainly for small expenses such as parking, buses, and subways. It's completely fine not to bring any. Your route is basically the same as mine, just in the opposite direction.

It's better to bring some cash. 300 pounds should be enough. 100 pounds is also doable. But you have to bring a chip card, because many places don't accept magnetic stripe cards, such as the subway.

Bring a debit card and take as much as you want.