The smoke comming from your exhaust will be the result of oil getting past the seal on the turbo - there are several causes:
Too thin oil/incorrect oil used
Removing of the cat
Turbo seal U/S.
If the seals are weak then any turbo car will start to smoke if left for a long period of time at idle - it is not good to do this just as it is not good to thrash a turbo when cold and not to allow the turbo to cool down before switching off the ignition.
You need to do go out for a longish run with the Coupe, make sure that when normal op temp has been reached then give it is some welly and then take the car to the MOT station, get them to test straight away before the cat cools and more oil leaks in to the cat etc. You should then pass the emissions for the test.
Should the turbo be fault then a full turbo service shall be required which means that the turbo needs to be removed and sent to a reputable turbo dealer/servicer - it should not cost more than £200 for the service, you may have to pay some one to remove the turbo but that should cost you no more than 3 hours labour to remove and refit.
Some owners at this point choose to change their turbo for a Hybrid which is a standard turbo with a collection of parts from other turbos made to help with spool up, higher boost reliability and service life - if you remain with the same compressor wheel then you will have the same amount of power but just delivered diff - see the FCCUK forum as I have listed a significant amount of information on the subject.
Also it is very important to only allow those garages to service or repair your Coupe that are specialists with the 20v engine - if you dont you may find major problems later - again go to the FCCUK forum where I have listed a load of specialists and their locations on a map for all to id where the nearest specialist, we have a lot of members in Scotland so also ask around.
Hope this helps - any problems or further questions drop me a line
For ease I have linked some info for you below -
Fiat Coupe service/repair/tuning specialist location and contact details list
Fault/how it works list - scroll down in section to see about Turbo's etc