Andrew Brook submitted this to the Crossovers Forum in Facebook:
In "The Kipper and the Corpse", a guest at Fawlty Towers - a Mr Leeman - dies whilst at the hotel, with (genuinely) hilarious consequences. Guess what happens to another Mr Leeman while flying to Boston in an episode of "Cabin Pressure".... (not much luck, that family!)
"Cabin Pressure" was a radio series starring Stephanie Cole and Benedict Cumberbatch. So for the purposes of the Toobworld Dynamic, it doesn't work to say that they're related.
But we can say that they're the same man but from two different fictional universes!
In the 'Fawlty Towers' episode "The Kipper And The Corpse", no first name is given for Mr. Leeman, so why can't it be Hamilton as it was in "Boston" episode of "Cabin Pressure"?
As to the fact that two different actors played the Leemans, it doesn't really matter since we can't actually see Hamilton Leeman in the Radio Universe. As to the difference in voices? Maybe he had a head cold and was affected by the high altitude.