A rigorous debate overnight and thanks to all for that. Full disclosure on our thinking / planning to return home at this time; it‘s been suggested that we delay a while which is understandable but more than an irritation; the main purpose is to visit the in-laws, both in their nineties and who the missus hasn’t seen in 2 years. They’ve battled well in the last 18 months, have had 2 vaccinations each and are extremely safety-conscious themselves. Also, the missus works at a university here so her next opportunity for a visit is not until Xmas.

Full disclosure on our plans:-
• As mentioned we’ve had 2 x Pfizer vaccinations administered in April and May;
• We are required to travel with a negative test result less than 72 hours old;
• We’re flying Icelandair who require all travelers regardless of origin to show a certificate of full vaccination and also require masks to be worn throughout the flight. Iceland is on UK’s green list of countries;
• We are on the ground for a 90-miute layover in Reykjavik but do not leave airside;
• We arrive Heathrow and will go through UK immigration checks and procedures;
• We’ll have a rental car booked and will travel direct to our family hosts in England to where three-pack testing kits will have been sent to comply with days 2, 5 and 8 tests required by UK government.
• Our family hosts live in a rural area with low infection rates and have had one vaccination and possibly a second by the time we arrive.
• Assuming the required tests show negative we would be free to leave quarantine after day 5 and travel anywhere in England.

Now we get to the point of my original post – the different rules currently in place in England and Wales. After day 5 our plans will be flexible, circumstances and rules in both countries could well have changed for the better with a further relaxation of restrictions. Otherwise we could just stay in England or perhaps visit the old folks but stay outdoors and at distance.
But why is Wales not satisfied with the day 5 release given all the other precautions having been observed? Merely in the interests of caution I suggest because the data is the same as in England and Wales have the best figures in the four home nations.

If we go we will arrive having proven we are not carrying the virus which is better than can be said for 63% of Wales' population that is not fully vaccinated; today's figures : https://www.bbc.com/news/uk-wales-55855220 )