arcon

We don't particularly mind it and don't care if te dash light is on - just not sure if it would cause any consequential damage if not repaired or if we can just put up with it....
I'll list the problem

Coil pack went couple of weeks ago - had to drive car a mile home over certain revs so keep it from cutting out and the juddering was mad! Think this damaged the cat c.
I think this because there was a tinny sound coming from below the down pipe after.
The EML is on - code reader states cat c effeciency low.
Pretty sure it's not just a sensor issue as now when driving there is a low beasty sound which comes from cat (below gear stick area)
On start up you hear it rattle.
On idle and driving you hear a rattle coming from it.
There doesn't seem to be any loss of power or anything like that.

Your thoughts are welcomes and appreciated...

It would seem replaceing is easy enough though....? You've got the exhaust manifold connection to the flexi pipe then connecting to cat c then connecting to rear section so just a number of bolts and new gaskets...
But if it's not gonna cause any further issues I'd rather just leave it until December when it's mot is

JFB Tech

It shouldn't do any physical harm unless the catalyst monolith breaks up more and blocks the exhaust. It'll obviously need replacing before the MOT, if it's breaking up and/or fouled from the misfire then it won't pass the emissions test. It'll also fail for the EML being lit.