Speaking as a PAX that has been using LHR + LTN to IOM for about 21 years and came back down on dear old MIMA on Tuesday ...
When BA bought Manx last year, I was heard saying (often) "They only bought the LHR slots, nothing else." Thus far, I have seen nothing to disagree with that.
BA have been buying UK regional airlines ever since when, they do it to get rid of competitors and take their slots for long haul. If this is not the case - then someone will advise me very soon now!
Oh yes, and I do remember the Viscounts!