I heard a fascinating interview today with the lady who worked as Peter Sellars' P.A.for a year.
She said that when he had to dicate official correspondence, he would always adopt a comedy voice, it was his way of getting to grips with things he didn't like doing. he also indluged in comic voice phone calls with Spile Milligan, and the Earl of Snowdon, who was personal friend.
Although the timescales are wrong, he could have based the look (dead ringer!) and funny voice (he's Portugese) on my previous manager at work - who acted like Clouseau as well - which is great for a comedy film series, not too hot for magaging a bunch of adults in an office!