passport valid for length of stay but not 6 months

Why not just renew it. There is plenty of time and it would have to be renewed anyway. I hate having little details like that on my mind when I travel. And sometimes it is the little details that mess up a trip.

Not enough time to renew before trip - that's the complication.

Even paying to have it expedited

Exactly how much later this winter and how little time does the person have to renew?

You might take a look at this forum discussion in which someone says they got their renewal in 3 weeks, much faster than the website said: https://community.ricksteves.com/travel-forum/general-europe/on-line-passport-renewal

A few years back our son was taking his daughter on a trip. Her passport was expiring on her birthday, the day they were arriving at their destination. Neither he nor his wife had even thought about their daughter's need to renew her passport. They live in Salt Lake City. They were able to expedite the renewal by making an appointment and going in person to the appropriate agency. They got the passport within a week. I'm sure that could also be done in Seattle.

In fact, this link has the details of how to do it including phone numbers: https://travel.state.gov/content/travel/en/passports/get-fast/passport-agencies/seattle.html

I hope it all works out.

I agree with the others - it's not worth the risk. This person should not have any problems - the last time I renewed my passport, I received it in 3-4 weeks.

There is no risk. Unlike other countries, the UK has no six-month passport rule and only requires that a passport is valid for the duration of the stay. The official UK gov website confirms this.

https://www.gov.uk/uk-border-control/before-you-leave-for-the-uk

The UK only requires passport validity for the duration of the individual's stay in the UK. That's it. There is no need for 3 months/6 months validity beyond or anything like that, nor a reason to fret over the issue. This is after all exactly what the UK goverment itself says.

If for some reason there is any grain of doubt, one can check the IATA TravelCenter for necessary documents and document validity -- https://www.iatatravelcentre.com/ -- this is the database the airline themselves will use to check documents.

There is a huge risk in the timing of the passport renewal efforts. I would not start a passport renewal if I didn’t have at least 4 months time before my next trip. My renewal time last spring was 16 weeks. I know that processing time has improved since then, but that experience has made me wary.

As long as the passport is valid for the duration of your stay, you will be fine. One thing to consider is the covid restrictions which seemingly change every day and whether you will need to isolate/whether your passport is valid enough to accommodate that.

You shouldnt have any problems in the UK. However, to avoid any possibility of issue, just renew. There are pleny of expedite services that will help renew it quickly. They might cost a little (170-230 USD, depending. I'm sure there is a bigger range of fees than that even) if that is a factor.