Whether you are legal to use Black/Silver plates for cars constructed after 1st Jan 1973 seems to be a bit confusing as various websites give conflicting advice, the statement below is taken from the MG Car Club:-
Following the change in definition of a historic vehicle for vehicle tax exemption purposes in 2015, an issue was identified in the regulatory requirements for the valid display of a black and silver number plate. This resulted in an unintended consequence where any vehicle over 40 years old and registered in the historic tax class would be permitted to display an old style black and silver number plate. This was despite the law previously requiring all vehicles first registered after 1 January 1973 to only display the yellow and white number plates with black characters.
As this was never the intention, DVLA have sought to rectify this through a legal correction which will shortly be implemented. The change seeks to prevent any vehicle constructed after 1 January 1980 from the ability to display the black and silver number plate despite being recorded in the DVLA’s historic tax class. Those vehicles with a construction date prior to 1 January 1980 will continue to be able to legally display black and silver number plates to avoid any undue costs of replacement.