How long can you stay in the Uk with a US passport

Appears to be 6 months.

https://www.gov.uk/standard-visitor

As a tourist (not working) it is 6 months maximum in the U.K.. It is the U.K., not England, Scotland etc so this is a total count. We have U.K. passports, not English etc.

We have U.K. passports, not English etc.

so far

The UK operates as a single governmental entity for border control, and you are allowed "up to six months". to travel England, Wales, Scotland, and N. Ireland. The UK is not part of the Schengen Agreement.

There is also an agreement with Ireland, the Common Travel Area (CTA), which for the most part allows free travel between the UK and Ireland.

It's six months. Just make sure you have a general idea or when you are leaving or have a return ticket and don't carry anything that can construe looking to live or work in the UK.

I've seen immigration officials pull aside people if they feel they might want to stay in the UK and not just on holiday.

The amount of time is discretionary, although people without any unusual pattern in their past immigration record to the UK are unlikely to receive a less time than 6 months.

Less than six months. If you stay six months you need a visa: https://travel.state.gov/content/travel/en/international-travel/International-Travel-Country-Information-Pages/UnitedKingdom.html.

This point has been brought up but....while you are allowed up to six months you aren't guaranteed admission. It is still up to the immigration agent.

I have been asked in the past about my travel plans, return ticket, finances--as to how I will pay for things, where I will be staying, and the like. And that was for a two month trip.

More than likely, as a US passport holder, you'll use the egates and won't have to talk to anyone.

I don't know how it works in the UK, but as a UK resident visiting the USA, I'm entitled to stay for 6 months, but if I don't leave on or before the date on my visa waiver, I have overstayed and can be refused entry in future.

It is six months. If you go through Heathrow US passport-holders can use the e-gates, so you don't come face-to-face with an agent. If you come through Ireland your passport won't be checked on arrival to the UK.

US passport holders are one of the largest groups of overstayers in the UK (the reverse may well be true but I don't know).