This was written by a health editor based on ONS data. The ONS can easily break down the data for each of the 4 nations but has chosen not to do so.

So, Scots are increasingly lax on masks too?

Nope.

The London School of Hygiene & Tropical Medicine has been monitoring behaviour changes in terms of facemask wearing and social mixing.

Notably, for the week-ending 29 September 2021, with rates falling slightly or flat across the UK, they noted in their data:

Self-reported facemask wearing for those who have at least one non-home contact appears to have reduced below 70% in England, though this overall figure masks differences by age. Reported face-covering wearing has stabilised in the over 60s but continues to fall in younger age groups. The use of face-coverings has remained high in both Wales and Scotland (> 85% of participants), where use in certain social settings has remained mandatory.

https://cmmid.github.io/topics/covid19/reports/comix/Comix%20Weekly%20Report%2079.pdf

A week later infection levels begin to climb in England

Then for week-ending 6th October, they report:

There has been a sharp decline in reported use of facemasks in Wales this week, but this is likely due to a smaller sample size. We will continue to monitor this in the following weeks.

https://cmmid.github.io/topics/covid19/reports/comix/Comix%20Weekly%20Report%2081.pdf

And for week-ending 13th October, the latest, they report:

The decline in face mask usage in Wales noted last week persists at approximately 75%. Face mask usage in England amongst those 18 to 29 years old who have reported contacts outside of the household continues to decrease.

https://cmmid.github.io/topics/covid19/reports/comix/Comix%20Weekly%20Report%2081.pdf

On October 16th, the infection rate in Wales surges and continues to climb in England.

Mask-wearing trends in Scotland and northern Ireland are not mentioned so stable. Rates flatten and appear to stabilise.

Health Warning: Other factors may apply.

Source: https://cmmid.github.io/topics/covid19/comix-reports.html

While I don’t usually go much for anecdotal evidence, I’ve seen 100% compliance in local stories and I’ve been told of almost 100% non-compliance as soon as you cross the border.