bumf

Is an example of upper-class British English.

You'll sometimes hear people referring to "U-" and "Non-U" English - they are talking about Upper-class and Non-Upper-class usage.

These categories were introduced by the Birmingham University professor Alan Ross in 1954. The U-English is spoken by the British aristocracy as defined as the roughly 80,000 descendants of the 150 landowning families that were titled before the industrial revolution.

Today Upper class English is mainly spoken by members of the royal family, old Etonians and ageing Oxford and Cambridge professors.

The upper-class English accent sounds rather different to Non-Upper class English:

In British aristospeak:

"Lost power of the British Empire" would be spoken so:
"Lorst pah of the British Empah"

At the other end of the scale stands London (Cockney) speech, whose prominent feature is the 't-glotalling', which means skipping the 't' in many words.

Instead of
"There is a lot of it about" you would hear
"There's a lo' of i' abou'.

Here are few more examples of "U" and "non-U" vocabulary:

preserves = jam
bumf = paper documents, junk mail, corporate news
brill = brilliant
for yonks = for a long time
bolter = husband or wife who bolts from a marriage
bounder = person of anti-social behaviour
crispies = money

(Source: Peter Huuck, http://Englischlehrer.de)