Mine failed on emissions last year. Added some Forte Injection cleaner and took it for a run the night before the re-test. Passed ok next day. As DLK said, clean out breathers, check plugs, and it will go a very long way to improve readings. DLK did mine late last year and along with regular oil changes i am not expecting any probs with mine in a couple of months time when i take it in for test. 

So did you take any of the advice that was given to you before you had the cat diagnosd as being scrap?

I suspect not but hey ho you got the ticket, and a large bill.

Change the engine oil and filter and air filter. Make sure oil is not being blown through the breather system in the intake and being burnt. Give the car a good blast just before going to the test site and get it properly warmed up. If the worst comes to the worst, there is an oil addative available from motor factors.
Works for me!