Thanks for that link.

Checking now has given the results for the London automatic monitors

ozone 9 reading low (8x1,1x2)
hourly mean NO2 11 reading low ( 9x2,1x1,1x3)
max 15min so2 6 reading low (6x1)
24hr mean pm2.5 1 reading low ; 8 reading moderate (1x3, 3x4,4x5,1x6)
24hr mean pm10 1 reading low ; 6 reading moderate (1x3,4x4,1x5,1x6)

Given the major health concerns associated with particulates, I think
the alert level of the BBC forecast (wherever it is derived from)
should have been higher , in line with the airtext warnings.