Can anyone please tell me if my cat converter needed replacing on my Ford Fiesta 1.25 zetec does it have to be done by a ford mechanic?

A replacement cat converter is very expensive and it is unlikely the cat needs replaced. Is the engine warning symbol lighting up? If it is the chances are that the sensor on the cat is either dirty or faulty.

The best way to determine if your cat is faulty is to have the exhaust emissions checked this will show if the cat is working properly or not.

A replacement cat can be fitted by any exhaust center, but expect to pay big bucks if you have to replace.