I think there is also the issue of 'balance across the piece'. If HIGNFY had a number of party leaders or similar senior politicians scheduled to appear during the EU Election Period, they would have achieved balance over that period. If Heidi Allen was the only party leader (or senior politician) booked for the shows during that time, it would be trickier.
However the argument about the EU elections potentially not happening is a pretty poor one. There was always a reasonably strong likelihood that EU elections were going to happen once it was clear the UK Parliament wouldn't support a 'No Deal' Brexit.
I do wonder if this is an Indie production company thinking they could sail close to the wind, and the BBC Editorial Policy department exerting some control.
As somebody from Editorial Policy was present at the recording, according to the statement from Hat Trick, I'm more inclined to think it was a cock up than conspiracy.
Yes. Indies don't just get commissioned and make the show of their own free will. The BBC commissioners ultimately sign off guests, content, pretty much everything. Somewhere at the BBC something went seriously wrong with their own editorial policy. I highly doubt this is Hat Trick's fault.
Considering Heidi Allen was listed as appearing in TV Choice which is printed over a week before the recording it's surprising that nobody within the BBC spotted her booking prior to the recording. Presumably had it been spotted and flagged it up as a potential issue to Hat Trick prior to recording (even if only when attending the recording) she could have been substituted.
Ref the BBC website it looks like the TV guide has now been updated to list the Graham Norton Show.
"Listen, we've all got something to bring to this conversation, but from now on what I think you should bring is silence." - Rimmer