And I’m a big fan of any suggestions that encourage visitors to get out of the usual suspects like York and the Cotswolds. There is so much more to discover almost anywhere you look and in many you won’t find many of your fellow countrymen.

OK - say I want to visit Oregon and its suggested Maine is lovely. Of course -- it is. And if the OP had asked for suggestions on what areas of England to visit - East Anglia, and Dorset, and Northumberland and lots of other lovely places would be recommended. But I read the OP to be asking specifically about London, York, Cambridge, Oxford and the Cotswolds and it seems they had put some thought into their trip and may have reasons for choosing those areas. If they are open to dropping York, Oxford and the Cotswolds and looking into other regions - then we can help them re-design the itinerary . . .

Maybe OP doesn't realise there is so much more, so many less touristed areas in the UK, which are just as lovely if not more so than the usual suspects.
We so often see York/Oxford/Cotswolds, or Edinburgh/Skye. Is it wrong to suggest another option? Spread the load a bit, and maybe even give them a nicer trip as a result? Possibly even a more relaxing trip given the age of the driver.

Oregon and Maine are a continent apart so hardly a fair comparison.