I own an 03 plate fiesta 1.4 TDCI which I believe should be in the band C but the tax disc reminder says that it is in band D with 121g/km. I believe that this is the wrong figure, is there anything I can do about it?

Carnut

See below

http://www.parkers.co.uk/cars/road-tax/?deriv=22781#manu=2514&model=238&deriv=22781

Bear in mind it's not necessarily the date of registration that matters. If your car was an 02 model that did not get registered until 03 then it may have the 121g/km engine setup.