The UK Blu-ray has the correct title Basil The Great Mouse Detective printed on the disc itself as that's the
official title in the UK/Ireland
Disney themselves list that's the title for the UK/Ireland.
UK DVD disc menu has UK title as does the opening credits title card on screen
The reason why the UK Blu-ray disc menu and opening credits title card has the USA title is it's the 2012 USA Blu-ray file reused on the UK Blu-ray
Disney UK was meant meant to do a UK encoding of the disc menu and opening credits card title for 2015 release to match previous UK Cinema and DVD/Vhs releases but decided to just use the USA Blu-ray file.
All they did was print the UK title on the Blu-ray disc and amaray packaging.
View attachment 403859
The correct title IMO that should of been used is what the disney animators originally wanted and that was Basil of Baker Street
USA changed it to The Great Mouse Detective and later in 1992 to Aventures of the Great Mouse Detective and then in 2010 back to The Great Mouse Detective
UK has had the title as Basil the Great Mouse Detective since it's UK/Ireland cinema release in 1986 and used with later UK VHS/DVD/Blu-ray releases
The opening credits title card on screen in UK/Ireland Cinemas in 1986 was also Basil The Great Mouse Detective