It is you and this other person that are making this claim.
Provide the evidence to support your claim.
Or, just for fun...name 10 other genuinely "right-wing" figures they have on.
Alternatively, the fact that the BBC is so bad at finding a broad selection of conservative voices to put on shows like Question Time that they keep on having to invite Nigel Farage back is a good demonstration of how their political leanings are causing them to fail at representing conservative views. I'm sure I've read a damning analysis of the BBC's process for finding conservatives to invite on and its failings along these lines.
As for how many other guests did they invite? Go and look it up, they have a publicly disclosed formula for which views gets represented and it's based on prior election performance and current polling during election cycles. Which is why it's so funny - it's just a nonsense to complain about the number of right wing guests.