Ah, that famous academic, Bulldog ...
According to
https://en.wikipedia.org/wiki/Oxford_University_Police "The Oxford University Police, or Oxford University Constables were popularly known as Bulldogs". Presumably someone at Beagle was an Oxford graduate and made the connection.
When in 1952 the Air Council was considering names for the RAF's new transport, suggestions received included Bison, Bullock, Bulawayo, Boxcar, Buffalo, Leviathan, Mammoth, Yak and - my favourite - Holdall! They eventually decided to use the Manufacturer's suggestion, and it became the Beverley.