My 1.8T is on long-life.... I've searched around and there seems so much conflicting advice regarding suitable oils at what mileage and all that
Look here -
http://www.golfgtiforum.co.uk/index.php?topic=65779 
And get it OFF LongLife!

VW gave me two choices: Their Quantum stuff for like £40 and their "special" one for like £65 for big 5L.

Did you have the letters M U & G tattoed on your forehead? Those are truely shocking and scandalous prices!!!!! Name and shame the stealer - because that really is robbery at those prices! What, exactly where they offering?
Garage I've got doing the work has said they use a "Carlube" product or I have the option of something pricier (might have been a Shell type), or indeed I supply something myself.
'Garage' and 'Carlube' should NEVER be used in the same sentance - and so-called garage which uses Carlube crap should best be described as cowboys! Carlube is rubbish, utter rubbish - and I bet Tesco Value oil would be better!

WTF any 'professional' workshop is on if they think that Carlube is acceptable is truely beyond me! No wonder the motor trade has such a bad name! For the record, Carlube oils do NOT have any Volkswagen approvals, dispite what they say on their website. Do NOT use that sh!t in any Dub!
Where should I get it from and what product?
You need an oil approved to either 503.00, 503.01, or 504.00 - from a quality European oil company.
HTH