Failed MOT emissions Audi A3 investigate or get rid?!

[Shellnoidea]

Sorry but I am pretty clueless!! Got a 2003 Audi A3 that Ive had for about 5 years, never a problem except recently changing front bearings. Failed MOT today as Emissions test had to be aborted as too much smoke, engines clean so no oil leak but car had 5 pints of oil put in during test which disappeared so they said its burning oil somewhere & best I could hope for was £70 scrap as wouldn't be financial worth it to try fix it! Do I try a cat cleaner?? Just can't quite believe it's the end of the road for such a lovely runner when it doesn't sound like a knackered engine, any help, ideas or things to check would be greatly appreciated!!