I too was a little surprised it was so many.
The figure of 8,000 was estimated using a baseline of those who were 98+ at the time of the 80th anniversary of VE Day in May last year i.e. at least 18 in 1945, which was the official minimum age for conscription. Now, nearly a year later I should think the number is significantly less.
The previous estimate was made in 2020 and the figure then was around 70,000 which indicates how rapidly their numbers are decreasing.
There’s around 16,500 centenarians living in the UK, another surprisingly high figure.