Infection rates are climbing steadily in England and surging in Wales. They’re pretty much flat in Scotland and Northern Ireland:
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.
For example, latitude? Average minimum temperature? Wind chill? Last winter, walking the dog on a chilly day, I put mine on, though a hundred yards from the nearest human and in a wind that would disperse your aerosols instantly. Joking!