Loop of Merry Olde England including North Wales Itinerary Thoughts

Can only speak for my areas of knowledge, but there's no way you can drive from Keswick and do Hadrian's Wall, Beamish and Durham all in one day.

The only "slower" day that you have us day 3.

Day 2 would be difficult to fit in a full day.

Day 8 is an itinerary for at least two days. Ditto day 11. Ditto Day 21. The V&A is the geographical outlyer.

Day 15. Beamish is great, but is difficult to squeeze into a day, so no time for Hadrian's Wall.

Day 19 York to London to Kew, presumably via your hotel won't give you much time in Kew. Check Sunday train travel closer to your travel date, as there maybe engineering works that will delay your journey.

We have done a similar trip. You may be able do it if you are gung ho. Remember to breath. Looks like you have avoided back tracking for the most part. We really enjoyed Wales and tried to visit most of Edward's Castles. We stayed in Betws-y-Coed which is very Fairy Glen. You are hitting most of the must sees. We have seen most of these but we spent a total of 30 days in 2 trips to do it. Look at the National Trust UK online site...it might help you visualize your trip. They have a Touring Pass for Couples for 14 days at 57 pounds.
They do England and some sights in Wales. Be sure to get a CADW pass if you want to see the Welsh Castles. Bon Voyage.

akkejakke: Durham is end point (dinner, sleep only), but understand the distance issue

jennifer: Day 2; we'll ask our friend but what would you suggest is doable and of interest?

Day 3 is usually when jet lag hits.

Day 8 is more wish list (ideas?).
Day 11 realize, what you cut?

Day 15 Three years of Latin inUpper School (High School in U.S.), Hardian's Wall may win out.

Day 19 wondered about Kew, which is why I said maybe some street markets.

Day 21 Prolly cut Victoria & Albert

kathleen: appreciate the tip on National Trust site and CDW

Please never use the phrase Merrie Olde England out loud to any British people you meet on your trip, especially not during the Welsh bit... I don't think you'd make yourself very popular.

"Day 1, 19.07 - Arrive Heathrow early, 8ish. Train > Windsor to see the Queen"

The train does not go from Heathrow Airport to Windsor. It is a short bus ride from Heathrow to Windsor. Follow the signs inside Heathrow Airport upon arrival to find the bus station. There will be a ticket window from which you can buy two tickets to Windsor. (The person who sells you your ticket will tell you your bus number.)
It's not far, so won't be expensive. About seven to ten pounds per person.

Exit through the glass double doors and sit on a bench while waiting for your bus to pull into the stalls.
Your bus driver will get out of the bus, take any luggage/bags and put them under the bus in the storage lockers.
Likewise, he'll get them out for you when you get to Windsor. There is luggage storage at Windsor Castle, so you can stash your things while you tour it.

"Day 21 - Tate Britain, Victoria & Albert Museum, National Gallery, British Museum"

No way you will be able to do all of this in one day.
The Victoria and Albert (V&A) Museum took us two days to see.
The British Museum took us three days, and we didn't see nearly all there was to see.

I suggest you skip your Sunday trip out to Kew and move one of these museums to Sunday afternoon.
This is definitely the thing to do if it happens to be raining on Sunday!

Unless you are in a check box ticking mode and just driving past places Day 8 will be nigh on impossible. I know and love all the places you mention for that day - having grown up in the vicinity - and they deserve more than a view through a car window.

It is obvious that you like or love gardens. In that case, a quick whiz through Hidcote will take two or three hours, more if you explore it a bit. The introductory talks on a rickety chair in a circle under th trees (included) are really good. The restaurant has pretty good food, too, in a great setting.

Day 6 is impossible.

Oxford will take a few hours - go in the afternoon to have a chance of visiting any of the colleges, not at exam time.

Bath can be all day, or at least a fair chunk of one.

Blenheim Palace is a half day at least, to say nothing of the gardens and the estate.

It doesn't seem that you have left any time for the travel between these places, which in itself will take quite a lot of time.

Day 10 - probably too much to get to Beaumaris.
Day 12 - Try and include Chester when going from Wales to Lake District.

You should find this previous post relevant:> https://community.ricksteves.com/travel-forum/wales/north-wales-itinerary

I can appreciate your wish to see as much as possible. Just one suggestion: for Day 9, you propose to stay in Ironbridge. This is a small village with an historic bridge and a museum (and not much else). I think you would find it more interesting to stop at Ludlow, which is a nearby market town with a huge ruined castle, beautiful buildings, and excellent restaurants. You can then head off to Ironbridge the next day.

Good thoughts all. I should have made it clearer - really my bad, right up there next to Merry (ie.) blah, blah - thx jane - that many days denote potential places to see, but not necessarily go. It is the way w{h}e sets out initial planning. We then winnie down to more realistic. So my bad as elicited some good feedback and brought to the forefront the impossibility of some of these days. Not to mention the help in winnying. Really am a fan of Sir Winston, so Oxford might drop off.

Sooo much to see. Feel the sands of time running down. Need the, "Whoa, whoa, whoa horse." Again any thanks, to all.

A couple of thoughts:
When in Westbury visit Stourhead - fabulous landscaping.
In the Cotswolds visit Bourton-on-the-Water - one of the prettiest villages in the Cotswolds.
In London see the interior of Buckingham Palace - it will be open some time this summer.
You have a very full program so these ideas may be should be considered as substitutes, not additions.

You say: Really am a fan of Sir Winston, so Oxford might drop off.

When visiting Blenheim you might see Winston Churchill's grave at St Martin's Church in Bladon near Woodstock, Oxfordshire - it's a mile or two from Blenheim's entrance.

When in London you could make a day trip to Chartwell, Winston's home. It might be a challenge without a car (which you definitely do not want to have while in London, but I am sure someone on this site will know how to get there).

"Day 9 - STOW-on-the WOLD > STRATFORD-upon-AVON > IRONBRIDGE [1 nt]
Day 10 - IRONBRIDGE > CONWY [2 nts]. Conwy Castle, Beaumaris Castle if time"

I would skip Ironbridge, absolutely. Just not worth the drive to see it, in my opinion.
Day 9, I would spend the night in Stratford-Upon-Avon instead.
Your plan to just do a quick one hour or so stop does not do the place justice.
A lovely town--the old part, that is--with good pubs and restaurants. You can do some lovely walks down the east side of the Avon. Walk south of the touristy areas to see quiet streets and old timber frame buildings.

You can leave here the next morning and go to Conwy.

I have hotel recommendations for Stratford-Upon-Avon if you want them.

The drive from Keswick to Durham is only two hours, (maybe a little longer depending on traffic) so that day is very doable.

As for Windsor, as Rebecca said there is no train, it's a 15 minute taxi ride to Windsor. If your plane is on time should should be able to get to Windsor by 10:30am. The Changing of the Guard takes place at 11:00am, if you are there in time you can see it a lot better at Windsor then at Buckingham Palace.
As for the Changing of the Guards at Buckingham Palace, you would have to get there at least an hour early to be able to see anything. If this was my last day I wouldn't want to stand and wait for it, instead walk around the corner (as you face the palace go to your left) and go through the Royal Mews, see the Queens horses and carriages.