There was nothing wrong with the model or the forecasting, they were obviously told to change it
errrr....
The Powers That Be can (easily) change the specified minima/maxima for any given situation, so long as the new value remains inside other legal / regulatory limits that may apply. They already did this - by going from 2000 to 4000 micrograms/cube (with additional caveats). They did
not need to get the VA forecast 'adjusted' as well. IMHO it would have been extremely foolhardy to even try to do so: someone could easily have other, more accurate evidence and/or might want to saddle the originator of the request/order with
all the responsibility (and potential blame). In this situation, a leak to the media would be a virtual certainty! For a recent example of this, see Climate Change 'emails scandal' at the University of East Anglia. A bit of tinkering with climate data and months later, after an external enquiry and at least one Severely Career-Limiting Move, they're still chipping brown solids off the fans! Especially with this recent example to learn from, I'm surprised the Met Office has so far failed to come clean about the forecast!
So why were the limits
and the VA forecast both adjusted, at very similar times?? (I still favour cock-up over conspiracy but have no better information myself.)
That said, it's also quite entertaining to watch the various regulators' heads popping above / below the parapet, depending on whether they reckon they'll catch blame (or have to take responsibility!) if ultimately something goes legs-up.