Am not sure what part Cecil Parkinson played in the matter but it was Air 2000 c1990 which put an end to the ludicrous idea that transatlantic flights could operate only from Prestwick. (Although the silly 7-8 minute lob across Ayrshire was quite fun for the pilots!)
He was the Transport Secretary in the Thatcher Government who when the Traffic Distribution rules were challenged by Air 2000 in 1989 instigated a review of the policy. On completion of the review, following a Court of Session victory for John Boyle and Air 2000, the rules were withdrawn and essentially the lowland airports policy from the 1970s and 80s was torn up. In early 1990 Northwest and Air Canada decided to move to Glasgow and that was the end of Prestwick's status as Scotland's long haul gateway. EDI's first real success came much later with the arrival of Continental on EWR-EDI.
It seems odd that given TS dropped the route on the A330 they'd really want to use the A330, given the capacity on the A330-200 is the same as the A310. (No, REALLY on Transat it actually is !) EDI's major issue is trying to fit a pint into a half pint pot for years with all the focus on shops and the new infrastructure pretty basic in the extreme. The chance to build a new Terminal facility on the location of the South East Pier and have a ten year strategic realignment and planned growth for decades ahead was passed up in favour of bolting a glorified walkway onto the current shopping mall and calling it progress. If Emirates turned up and offered to start flights Apr-2011, are you seriously saying that EDI would say thanks but no thanks? A way WOULD be found by shifting someone less glamorous along a few stands.