Do we need an International Driver's License to rent/drive a car in UK?

Not if it is in English

No. Not in the UK.
An IDP is required in Europe only in the following countries:

Austria,
Bosnia-Herzegovina,
Bulgaria,
Czech Republic,
Estonia,
Greece,
Germany,
Hungary,
Italy,
Poland,
Romania,
Spain,
Slovenia

It's an IDP (International Driving Permit).

No not needed BUT a good navigator is a plus to remind you to stay on the opposite of the road.

That and reading signage as you drive in a roundabout so you take the proper exit.

When I rented a car in Scotland, I noticed they put the steering wheel on the wrong side too. Diabolical! And shifting with your left hand and driving in the rain and great scenery and kids yammering "look at that dad". Wow! Good times! I loved it.

Thanks, all for your answers. I just got back from my trip and I can confirm that my US (Californian) license worked just fine. Beware the hidden charges though. I booked my rental through Expedia. I price compared with Booking.com and another website. Expedia was the cheapest for what I wanted (four door premium car). It was supposed to be $574.24 after including the extra insurance I paid for. I was charged $677 in the end (car was returned undamaged and acknowledged as such; we also returned the car with a full tank of gas). When I reached out to Expedia, they said that the fine print says there may be other charges. Even though I already paid for extra insurance, Alamo staff at the airport tried to hard sell me more insurance saying that the insurance I bought is not theirs and that I am liable for 50,000 pounds if there should be an accident. All in all, I think I will avoid booking through Expedia in the future. It is hard to compare pricing when I can be charged unknown charges last minute.

We had no problem driving on the "wrong" side of the road. The only part that was harrowing was the very narrow roads at part of the Lake District.

The rental car I'm currently driving was secured through Expedia (via AARP). We've not encountered any hide-the-pickle when it comes to fees as of yet; my attention has been raised now.

For future car rentals you may want to look at Auto Europe. They are a consolidator based in the U.S. I’ve used them many times and have always been happy with them.

When I rented a car in Scotland, I noticed they put the steering wheel on the wrong side too. Diabolical! And shifting with your left hand and driving in the rain and great scenery and kids yammering "look at that dad". Wow! Good times! I loved it.

Hilarious

Limos in London? Never heard of such a thing. Limo is an American thing - is your link to an American company?

You do not need an IDP.
You do not need one, no siree.
You do not need one in your car,
You do not need one in a bar.
No IDP for you, I say,
So pack your bags and fly straightaway!

Apologies to Theodore Geisel.

Limos in London? Never heard of such a thing. Limo is an American thing - is your link to an American company?

It's called spam, Nigel. Both our versions of English refer to it as spam.

And it's been reported.

Thanks jphbucks for a good laugh

Do visitors to the USA need anything special to drive there?