Treenifer got it right..I read an interview with Merton where he said that Deayton had to go because the show has to be about the news and not the host.
I think it would have died quickly if he had stayed on. Too bigger loss of credibility.
I think it is a particular case with satire that the satirist need a level of credability higher than other forms of comedy or else it just doesn't work.
At the end of the day he was naive enough not to pause with rolled up £20 note on one hand and prostitute in the other and say to himself 'I get paid large sums of money to take the piss out of other people's sexual shannaigans and folibles..perhaps this isn't the best idea.'
Little sympathy from this neck of the woods.