New Catalytic Converter fitted yesterday. Quite a lot of destroyed rubbish found in the old one. (Photo attached). Code reset and has so far completed sixteen miles and no yellow management light as yet. On previous times of resetting the code it has taken up to 18-20 miles to regenerate. Fingers crossed this time. The moral of this story may be, I should not have spent time and money attempting to deal with the P0420 Code by cheaper methods first. I.E. new sensors upstream and down stream, smoke testing, checking all joints etc etc. Followed lots of sound and helpful advice but eventually had to "bite the bullet" and buy the new Catalytic Converter. Not to worry, hopefully job done now.