Originally Posted by WHBM

Third Class was the normal accommodation (and thus did not have a downmarket soubriquet) on the railways in Britain until 1956. In Victorian times there had been three rail travel classes, First Second and Third, but the intermediate one was steadily eliminated, and the furnishings etc in third class brought up to its standard, so for many years there were mostly just two classes, First and Third. The naming was changed in 1956 to First and Second, and then in the 1980s Second became Standard.