"What is causing this decline? Are Christians less interested in academic study around the Bible these days? Are people taking up alternatives, or not taking up anything at all?"
The United Kingdom of Sodom and Gomorrah doesn't do Christian religious training.
Signs of the times.
Less church, less doctrine and less Christians is bound to mean less need for Christian Bible colleges.
Satan is winning more and more in the UK today so he is going to make sure there is less and less input of Bible teaching into society. He already holds complete power over Politics, philosophy, justice and morals that he destroys these to raise chaos in the nation.
Then there is the "National" churches the CofE and CofS which have the new motto "Ditch the Bible to keep the sin." This is Satan's religion called Liberalism. Their witness is one of ignorance, blindness and burlesque - any ludicrous parody or grotesque caricature of religion.
Finally God does not bless the nations which reject Him, His Son, His Holy Spirit and the Book, laws and doctrines which He wrote.