I know the majority of members on this forum are extremely knowledgeable compared to myself but I can only say about my experiences.
Several months ago my EML came on my 2.6 V6 CD and I got the same cat efficiency codes you have now. Finding money extremely tight, I did not fancy the idea of possibly having to get new cats.
I do a lot of very short journeys in my car which i am sure is not very good for the engine, usual 4-6 miles a day and a bit more during the weekends.
Someone on this forum suggested doing an Italian tune up to give the exhausts a good blow through to try and dislodge any build up inside.
Initial nothing seemed to happen and the light remained on until about 3 weeks ago, when all of a sudden the light stayed off.
The cars just had its MOT and the emissions were well below the legal limits. (although it failed on front wishbones, which have been replaced.)
May be the short journeys caused a build up of dirt around the sensors in the exhaust and the Italian tune up gave my exhaust a chance to clear itself, any way I am happy as it passed the MOT for this year.
Dave