My friends at 'Limn Historic' recommend the following:
"Derby Plating (in Derby, obviously) is the only place we use and the only place we would recommend. They charge fairly (although probably won't be the cheapest around) and provide a top notch service. Their turnaround time for large items (bumper etc) is usually 6 weeks, but this is a true time estimate and they are well worth the wait."
Derby Plating I have no connection but sought advise only from a reliable source ....