and here's another mate's guess:
Too many "coulds" in thsi riddle to make much sense but as you asked - how about Hearts and win a European final (note I didn't say the European Cup) for the first time?
I think this takes care of Man Ud who could end up winning the EUFA cup final (a trophy they have never won) by being knocked out of the European Cup.
Everton and City aren't in Europe so will have to wait at least a year and all the other teams are in Europe and could all conceivably win a European trophy they have never previously won apart from Liverpool who as everybody knows have won 5 European cups and 3 EUFA cups! Only problem I can't remember if Celtic have won the EUFA cup (I don't think they have) so I''m not sure why they can't do it - although they were in the Cup winners Cup final recently although why that should be relevant god only knows..
Oh hell, as they are in the EUFA Cup, I'll go for Gretna instead...
Of course there mioght be some Welsh or Northern Ireland team I haven't thought of...
Jeez, this is worse than work...
He was SO close. Then he headed the wrong way.....
Another clue, in fact one of the 2 answers required..... Aberdeen are the only other British team who can do IT - they are in the same boat as Everton & Man City in that they would take longest to possibly do it.
(I'll pm you the answer if you want - or post it up tomorrow if everyone wants it).