Red Pike is a classified United Kingdom government encryption algorithm, proposed for use by the National Health Service by GCHQ, but designed for a "broad range of applications in the British government" [1] Archived 2004-04-23 at the Wayback Machine.
According to the academic study of the cipher cited below and quoted in a paper by Ross Anderson and Markus Kuhn, it "uses the same basic operations as RC5" (add, XOR, and left shift) and "has no look-up tables, virtually no key schedule and requires only five lines of code"; "the influence of each key bit quickly cascades" and "each encryption involves of the order of 100 operations".
64 bits of key entropy are not considered secure anymore.
Given that Red Pike is a British encryption algorithm, its name likely refers to a particular fell in the western English Lake District.
In February 2014, the supposed source code for Red Pike was posted as follows to the Cypherpunk mailing list.