This punchline thus formed the basis for the phrase, but its usage is quite different.
The Mugss usage dates, I believe, from 1996 with Carol McKay and Kate Smith (possibly Penny Richards). They discovered that McVities' biscuits contained gelatine, and thus "bits of old hoof", which is obviously non-vegetarian. The AbFab phrase was thus pressed into service in a post-modern referential manner.
This expanded to be "Has the food got any hoof in it?" (ie, does the food contain any meat products) and then, given the sympathies of the users and the high junk level involved in Mugss life (costumes, bits of set) the phrase crept in scope to mean "junk". For a period a distinction was made between "Functional hoof" (hoof that has a purpose but is ugly/too large/otherwise despised, like a hideous toaster), "Structural hoof" (hoof which could not be disposed of, like revolting student-house wallpaper), and "Temporary hoof" (hoof that has a purpose for 1% of its existence – costumes being the most obvious example) but we all then got jobs.
The word then spawned "hoofy" and "hoofing" in the marvellously flexible way that English does.
A real piece of old hoof was brought back from Exmoor by Carol in 1998, to the huge amusement of the house.
Hoof should therefore be regarded as a noun. The verb "hoofing" and adjective "hoofy" are used occasionally, the former usually as "hoofing around".
Hoof was used briefly at Cable & Wireless in 1999/2000 in project management strictly as a noun, again to refer to elements of the specification from the technical department as being sub-optimal.