Five Week England/Wales Itinerary

I think it is way too ambitious. You are trying to hit too many places in too few days.

Cambridge can be done as a day trip from London. I took the London Walks. It was excellent. (I don't think it is given in the winter and next summer's schedule isn't out yet.

I do think not having a car would make some of these very very slow to get around. If you have a car it would be quite easy. It isn't intimidating to drive in England as long as you avoid London and pick up your car in another city and/or ditch it prior to going to London. I've done this 3x and have basically driven around the country for a total of 6 weeks. Roads are generally well maintained, drivers more polite, and you get used to the opposite side quite quickly. Cornwall is rather "colorful" (extremely narrow lanes) but still a feasible place to drive if you are careful. I'd take driving there any day over my normal Los Angeles crazy :0! yes it would increase your cost for the trip, but it would allow for much more flexibility in seeing places.

That being said below are my suggestions from the places I've visited:

London - I would spend 6 days in London, then 2 more for your "day trips" . Brighton is just "ok" not really what I expected. The royal pavillion looks lovely from the outside but inside there isn't much left except replicated things since all of the furniture including most of the rugs is in houses that the royal family has. I found it really dull tbh.

With the remaining 27 days devoted to:

Liverpool

Chester

Hadrians Wall- I did this in like a day (but I had a car)

York - 3 days is good.

Lake District - 4-5 days- The Lake District is AMAZING! I'd recommend staying near Windemere/Ambleside . Personally the Lake District to me was the best place in all of England.

Cambridge

Oxford- 3 days should be ok.

Cotswolds - (quite dull to be honest) 3 days MAX. They have a really intriguing wild animal park you should check out- Rhinos and all.

Eden Project - This is way too far south I would cut out Cornwall entirely OR Fly there first if you are able ???

Seven Sisters

Lands End- I found this very dreadful (it is a mini tourist trap) and St.Ives is about 1,000x more interesting- they have some great arts and crafts shops that are authentic in St.Ives. St Michael's mount in Cornwall is quite nice if you really insist on doing Cornwall. Penzance is small but has great restaurants.

Black pool

Portmeirion - Wales

Snowdonia - Wales - lovely, massively large and spread out. 1 or 2 days depending what you enjoy doing. Skip "fairy glen" it is overrated--- my friend and I took 2 hours trying to not slip on moss to get to it. They have some very interesting neolithic sites that are kind of in the middle of nowhere and may require some good "duck boots" due to cow droppings/needing to cross fields.

Brecon Beacons - Wales- 1-2 days

Hay-On-Wye - Wales

Conwy - Wales - CONWY IS THE BEST! that being said it is super small and you can see it in 1 day or half a day. My friend and I (although we did have a car) did Conwy and Carnaferon in a day along with Beaumaris. I think Canafareon (yeah I'm probably spelling this oddly) was the best of all 3 castles, with Beaumaris coming in 2nd.

Llandudno - Wales . - lovely seaside area. I used this as a base when in wales. Don't miss Bondant gardens!!!! Which is not far away from Llandudno. 2 days?

Agree with Frank above re the London walks day trip to Cambridge. I've done it too and it was great. www.walks.com. They also do other day trips - to Oxford and to the Cotswolds. I have done their day trip to the Cotswolds and I enjoyed that - for me that would be enough time there - I'm another who finds the obsession with the Cotswolds baffling.

We did a four week drive tour of South Wales and England (didn't go to London or SE England). It was amazing. Here is a detailed review of our trip that includes lodging, restaurants and travel tips:
https://www.cruisecritic.com/memberreviews/memberreview.cfm?EntryID=599139

Your visit to Wales is in the North. We visited Conwy and Snowdonia on an earlier trip, it was great. Not so impressed with Liverpool. It was OK, but other places in England we enjoyed more.

South Wales is where my paternal ancestors came from and we visited the small village in Cardiganshire where my ancestor left in 1716 to come to America.
St. Davids at the SW corner of Wales is amazing. Also, Tenby is wonderful. South Wales is very scenic.

We stayed in Keswick in the Lake District (see my link for the great B&B). York was one of our favorite places. We loved the Cotswolds, staying in Chipping Campden (used it as a base to visit Oxford, Blenheim Palace (where Churchill was born) and Stratford Upon Avon. If you care at all about Shakespeare, Stratford is a must.

Bath is a must see, loved the Roman Bath Museum. You can still see some of the ancient plumbing that still works.

Durham, a bit north of York is another great city, as is Winchester in the South. We deferred going to Cornwall for that trip, now we plan to visit for one week next July. I think Cornwall will take several day.

Five weeks is a long time and you should be able to manage with that time. Still, you need to manage your travel time. Of our 28 days we only had three days were we drove more than two hours. Traffic is heavy in southern England, and around cities like Liverpool, Manchester and Birmingham. I would advise you to stay away from those cities. Chester would be a good choice. Don't even think about going near London. The traffic is awful, especially on the orbital around the city.

Make sure you drive an automatic with a navigation system or have a good GPS.
Don't do too many one night stops. We had a couple, like when we stopped at Haltwhistle to see Hadrian's Wall (or what is left of it) on our way from Durham to Keswick.

With the remaining 27 days devoted to: ... (18 places all over the country) ... Any observations on how I can hit the majority of the above over five weeks?

But you don't have 5 weeks because you gave that week to London. You have the 27 days you mentioned, even less if your arrival or departure days are in that 5 weeks or 27 days.

With 18 places from Cornwall to the Scottish border, and Wales, both east and west in both the far north and far south,that's a lot to do in 27 days.

Usually we count nights not days - it is usually more precise. With 27 days is that only 26 nights? Are your departure or arrival days in there? Heathrow? What time?

What a wonderful journey you are planning! I'm sure you can visit at least half of these places. It's important to take the time to experience these places and the people who live there. Hay-On-Wye might only take half a day while the Lake District deserves several days, for example. I'm also sure you'll want to plan a second trip and maybe a third.

I suggest you also plan some days for unexpected experiences. England and Wales are full of scenic roads, historic spots and little villages that will surprise and delight you!

Your northern destinations, for instance, are all pretty close together when driving, e.g. Conwy to Chester approximately 1 hour, then to Liverpool 45 min, to Blackpool 1.5 hours, to Keswick 1.75 hours, to Haltwhistle 1.5 hours. Visit some as stops-on-the-way or side trips from a home base, to reduce one-night stops (although I find one-night stops fine for some small towns).

Good candidates to be daytime "activity" stops include some places that others suggest dropping, e.g., Blackpool, Hadrian's wall, and Portmeirion.

In the south, I'd say the same about the Eden Project, Land's End, and the Seven Sisters, but they're more spread out and you haven't named anything that sounds to me like a real home base or key reason to go to this area.

Make your home bases in the places of most interest to you, so you know they're covered, while side trip plans can remain flexible. You are active walkers/hikers. Are you also relatively early risers who like to attack the day? That certainly helps to fit more in.

I’d throw out Blackpool. Chester is best done as a day trip from Liverpool and easily accomplished on the train. I also agree with slowing down. When I was in Newcastle, I waived north at Hadrian’s Wall but didn’t try to go there. I’d look at Newcastle/Durham/York for that part of the country.