Is this 8 day itinerary realistic?

Train to Oxford and rent car there.

Buy the RS England guide book and read it.

Forget the Lake District, you’ll spend far too much time in the car getting there to truly enjoy it.

ChatGP? AI. Wouldn’t trust it but I’m a Baby Boomer who has been to and stayed in various parts of England since 1972.

To make your itinerary a little more efficient, after you land in Heathrow, go directly to Oxford on the "Airline" bus. When you are done with Oxford and ready to move on, rent a car. Go to London at the end of your trip, but drop your car off before going to London. You really don't want to deal with a car either in Oxford or in London. I don't know about driving to the Lake District. Have a great trip!

We have been to London a few times so don't need to spend much time there but flights are already booked in and out of Heathrow.

You might consider taking the bus to Oxford from Heathrow immediately on arrival. It only takes 90 minutes. There is a group ticket for up to 4 that might work well for you.
https://www.theairlineoxford.co.uk/

You could get over your jet lag there and then pick up the car as you leave Oxford.

When you return, you could also drop the car back in Oxford and take the bus to Heathrow. If you want to stay in London at the end of your trip, you could drop the car off in Oxford and take the train back or take the “Oxford tube” bus.

I would not recommend this itinerary. You are not giving yourself enough time in the places you are visiting, and you are spending a major chunk of two days out of your eight driving. Remember you have to pack, check out of your hotel, find the new hotel and check in, and that is in addition to the actual driving time. How are you gong to see much of Oxford and Statford Upon Avon in that brief two days, which includes getting to the rental agency and driving. Oxford is wonderful and there is a ton to do there. You could get an overview on the day you get there, but that is all. Then the next morning, you go to Stratford Upon Avon (where I have not been, but I know there is a lot to see) and again you will get an overview. But you also need to drive to the Cotswolds that day. The Cotswolds is a huge area, but you won't have time to see much more than one village before you head off for the Lake District the next day. You will have just one full day there, enough for a a little hiking and a couple of dinners, then it's back in the car to get to London, where you'll have an evening after returning the car and getting to your hotel. It seems very rushed to me.

I agree with Claudia -- skip the Lake District. That will give you five nights for Oxford, Stratford Upon Avon and the Costwolds, which are all close together. You'll get a variety of sights without spending a lot of time in transit. A much better use of your time. I think that would make for a really nice trip.

No it is not realistic for the Lake District. Nor is trying to do Oxford and Stratford in one day.
And a car is useless in Oxford.
The last week in August is the last week of the summer school break and will be very busy in the Lake District. Four to five hours is optimistic to cross Birmingham and cope with roadworks. Then once in the Lake District traffic will be very slow because the roads just can't cope with the amount of traffic and car parks full to bursting point, not to say expensive as the authorities are actively trying to price out car borne tourism.
There is excellent public transport in the area.
If you must have a car in the south, then off hire it at Birmingham Airport and take the train.
On Day 8 the journey back to London by train will be half as long as driving back.

There are 13 Michelin starred restaurants in Cumbria, several of which are in very non tourist parts of the County, but three are in Ambleside and one in Grasmere.

I just don't think the Lake District is a sensible extension.

Forget Chat GPT. It may be physically possible to travel to all those places in the allowed time, but it sounds like a miserable trip. It makes no allowances for actually visiting any of the sites that make these places popular. Nor does it account for summer holiday crowds and heavy traffic- meaning many extra hours in the car staring at the tail lights of the car in front of you.

And it's very last minute trying to get accommodations in high season. I think you should consider scrapping the Lake District altogether and just concentrate on the rest, saving London for the end.

Thanks for the reality check everyone! Following the suggestions here we will save LD for (perhaps) a future trip.

Does this make more sense:
Day. 1 -LHR to Oxford recovering from red eye, walking around city center, meals,
day 2 - seeing a college and Bodleian library etc.
day 3 - rent car drive to Blenheim palace, and on to Stratford upon Avon, spend night here
day 4 - see a play, see the house Shakespeare was born in, perhaps Warwick Castle,
day 5 - drive to Cotswolds, spend days/nights 6 and 7 here,
day 8 drive back to Oxford and return car,
day 9 flight out of LHR
Question - is there scope to visit Bath just to see the Roman baths on day 8 and get to Oxford that evening? Seems to make sense to be in Oxford the night before our flight.

- I assume it is best to base one's self in one hotel in the Cotswolds and drive around to the other villages and towns?
-Realizing that we are very late to be booking hotels but still welcome recommendations in any of the above places. Restaurants as well!

Can you drop the car in Bath instead of going back to Oxford, then go on to London or Heathrow from there? There is a National Express coach that runs direct from Bath to Heathrow.

To me Bath takes more than a couple of hours but you should do what makes you happy.

I agree with the advice to take the bus to Oxford directly from Heathrow, and recover from jetlag there. You can take a local bus from Oxford to Blenheim Palace. Then take the train for the short ride to the Cotswolds (the stop is in Moreton-in-Marsh) and use MIM or another town or village as your headquarters to explore the area by foot (wonderful public footpaths everywhere).

I know that standard guidebook advice seems to be that a car is required to enjoy the Cotswolds but I've been there four times without a car and have been able to get around by bus, foot, and occasional taxi quite well. I will add a caution that the local buses are not super-frequent and can be somewhat unreliable, so if you're not ok with uncertainty you might prefer a car (a small one). My husband and I (ages 69 and 70) love walking village to village; stopping for lunch in a local pub is an added pleasure.
I think that Bath deserves at least one full day (two days are better) but if your priority is the Roman Baths then a half-day should be enough. Be sure to buy your timed-entry tickets before you go!
I can't comment from personal experience on getting to the Lake District but that seems like a lot of driving to get up there.
Have a wonderful trip!

Your updated itinerary looks mostly doable to me, but a few things to mention:

-If you're travelling at the end of this month, it's likely too late to get tickets to Bodleian Library- they go on sale a month in advance and sell out almost immediately. If you are still interested to go I would check right now.
-Stratford (upon-Avon) has so much to see I wouldn't try to fit in a trip to Warwick Castle as well. In addition to Shakespeare's birth house I would definitely recommend Anne Hathaway's house which is very well preserved and makes you feel like you are stepping back in time, plus has a lovely garden.

The only place you've mentioned where I've stayed overnight is Stratford-upon-Avon- we loved the Arden Hotel which was very centrally located (and close to the theatre if you're planning to attend a play)- we had a good experience there.

Your updated itinerary is much more doable. I hope you have a great trip!

I agree about Stratford upon Avon and Warwick Castle on one day, especially during the school holidays and around the August Bank Holiday. Both can easily be all day. Warwick Castle is really well preserved but it takes a boat load of money to get in and will be crowded - there are absolutely loads of things to do especially for kids, including the Trebuchet!. To try to rush it will possibly result in frustration.

Be careful, be very careful, where and how you park in Stratford upon Avon. There is a Park and Ride on the road from Warwick, and there is a multistorey near the river and the High Street, but it can fill up. If you try street parking read the signs really carefully - Stratford has a nasty habit of different rules on the two sides of the road. Read really carefully. Stratford has a little army of quite keen parking enforcement officers.

I used to live just a short distance away with frequent trips into and through both Warwick and Stratford upon Avon so I do know of what I speak.

Be careful, be very careful, where and how you park in Stratford upon Avon. There is a Park and Ride on the road from Warwick, and there is a multistorey near the river and the High Street, but it can fill up. If you try street parking read the signs really carefully - Stratford has a nasty habit of different rules on the two sides of the road. Read really carefully. Stratford has a little army of quite keen parking enforcement officers.

I always find that the big car park by the leisure centre has spaces. It’s just across the road from the multi-storey and also the loos at the leisure centre are handy to use. Then it’s just a short stroll into town.

We did Oxford, Blenheim Palace (Churchill was born there), Stratford Upon Avon and the Cotswolds some years ago. You need to rent a car to do that.
Forget The Lake District, you don't have time for that.
I recommend The Volunteer Inn at Chipping Campden for the Cotswolds. They have a great pub there and an excellent Indian Restaurant.
Rent the car after you plan to leave Oxford, parking there is outside the city. Also, when going to Stratford, you must park in the lot just outside the city.

You need 1-2 days to do Oxford, and 1-2 days for Stratford, as well as minimum of 2 days covering the Cotswolds. Blenheim Palace can be done in half a day, it is between Oxford and Stratford.