Why does catalytic converter block?
 
                Vauxhall Astra, 2002, 1.6 ,8V.
The engine light comes on, and when slowing from high speed, the car cuts out. I had the fault read and apparently there was problem with the Cat.
I had it cleaned out, the guys removed A LOT of light grey sooty residue which resolved the problem for a while.  Any suggestions what is going wrong?
            
             Neil
            
 April 2010