Yep, you're quite right. Thanks. Here it is.
http://www.npr.org/templates/transcript/transcript.php?story... At 00:20:40
"CLEESE: Yes, I do. And it just showed why he was such a wonderful impersonator. But it showed that in a very strange way because he'd overslept. And his chauffer Bert said, sorry, boys, Peter's overslept. I'll make you coffee. He'll be out in a bit. And we just sat there sipping coffee. And when Peter came out, he was still in his dressing gown or his robe. And he was apologizing for having overslept, but apologizing in a voice that was not his own. And suddenly, he switched into a rather sort of plumy upper-class voice and was talking to us like this as he walked towards us. And at a moment, he was talking a bit like that. And then he went into another voice, sat on the sofa and 10 seconds later, he was talking to us in his own voice. And see, we were the first persons that he'd spoken to that morning. He'd only just been up a few minutes. And we realized when Graham and I - Graham Chapman and I - sort of compared notes afterwards, we realized that Peter Sellers in the morning had to find his own voice.
DAVIES: So he wasn't trying to impress you. It's like somebody tuning in...
CLEESE: No, no...
DAVIES: ...A radio dial and finding the station.
CLEESE: There was a lack of real personality at his core. And the people who were very good impressionists are often rather like that. Similarly, people who write very good parodies but don't write such great original comedy, those people often lack a certain emotional life. They're very clever, their observation is good, but emotion doesn't inform their work in any way. So their work tends to be brilliantly observed, but not very - what's the word? - not very powerful. They don't tend to be terribly funny. They tend to be terribly clever. So this kind of personality type - a person who has a weak sense of their own identity - they're frightfully good at copying other people, whether it's other writers or other performers.
But we realized that Peter literally had to find his own voice in the morning. And to that extent, he was a sort of personality that he'd had to manufacture himself from different parts. And I - one of the Pythons was ever so slightly like that. And we could always tell when he had been spending time with one of his Beatles friends because he would have a slight Liverpool accent for the next 24 hours."