Well he tweeted his thoughts on his own platform - his personal account on Twitter, - not on the BBC.
That is a violation of his free speech, no?
The calls for objectivity and impartiality (from the BBC) would be a little more credible had the current chairman of the BBC not himself previously donated £400,000 to the Conservative Party and had also facilitated a loan (of around £800,000) to the disgraced former Prime Minister, Boris Johnson.