Reading the OP I would guess that it's the FGA readings that have caused the BG bloke to categorise the boiler as AR and cap off (permission not mentioned).
But agree with AWheating boiler is insured with BG, get then back to fix it.
Only guessing but BG bloke may have been at a loss as to what to do next. FGA readings out, clean. FGA readings still out doh!
There was no mention of the boiler being shut off, he just stated that he had in the report! It states "High emissions on maximum rate, cleaned still high"