What is the rarity and value of the introduction of the Advanced Passenger Train railway letter stamps?

by ray williams
(suffolk england)

These stamps were first printed with a white background for the inaugeration but was not used.

A better quality reprint with a Red background was used; Red,Black and Yellow 55p stamp was issued.
7th December 1981: Introduction of the Advanced Passenger Train.

A very accurate scale model will be made this year and will be available from next year.