Freelander Mk1 failed MOT on emissions

I've got a device that screws into the plug hole. The device then hooks upto my compressor. This is then used to pressurise the cylinder, thus keeping the valves closed. This allows the collets to be removed without the valves dropping into the cylinder.

The timing belt will need to be removed as will the cam shafts. It's a good few hours work. Is it worth fitting another cat first, just in case?

I was also thinking it may need another cat, i can hear a tinny sounding rattling noise coming from the cat when i slightly press acelerator, it's quiet when on tick over when i put my foot on the pedal slighty i can hear a tttttt noise, i stuck my head under the car and preesed the pedal with my hand, the noise is definately from the cat, is this normal or signs of a duff cat.

Just got the receipt out, i got it on 6th March so should still be under warranty, if it's not working as it should will they replace it or give me a refund.

As anyone tried stop smoke you put into the oil, a lad at the parts shop today said it works, i may give this a try tomorrow as it's only six quid.

I'd be trying to get the cat replaced before ripping the engine apart.
Maybe the cat was dropped before you got it?
Stop leak works by softening the rubber seals and O rings. It can work, but generally only temporarily. Nothing can take the place of new seals.

I have fitted a cheap cat and it hasn't performed for the mot before!

What cat did you replace it with, did it then pass after you fitted a new one?

Can anyone reccomend a cat and supplier as i've read online some cars fitted with cheaper cats fail emissions on the mot, when replaced with a better cat it then passes the emissions test, granted they weren't the same make of car.

Bought replacment cat from eurocarparts , but just not the "euro" cheap cat.