What is covered includes penis in animal's vagina or anus and animal's penis in human's vagina or anus. Oral sex with an animal will remain as legal as it is now (ie covered, where appropriate, by the cruelty against animals legislation).
Should oral sex with an animal always be illegal?
Yes, both giving and receiving
Only when it licks a penis
Only when it licks a penis or a vulva
Only when you lick its penis
Only when you lick its penis or vulva
Other (see comment)
Trivia note - in the 1980s, someone called unsuccessfully for one of the better sex education books to be banned because it pointed out in its section on the law that oral sex with an animal wasn't covered by the bestiality legislation. The comment was withdrawn from later editions of the book though.