Just came across this site on AnF which mentions SNARL-UP was never released
http://retroisle.com/general/publishers/anf.php
Unfortunately despite selling over a million copies, the cult following Chuckie Egg had received couldn't keep A'n'F Software afloat indefinitely. Snarl-Up for the BBC Micro never appeared and, finally, in 1985 the company went bust. Some remaining A'n'F-branded Electron stocks of Chuckie Egg and Cylon Attack eventually turned up as a free gift for Electron User magazine subscribers. When other development studios were being gobbled up by publishers, A'n'F struggled in vain to meet the demands of advertising rates and distribution prices.