J. Oliver's usage of the word 'bog'
From Tony Thorne, The Dictionary of Contemporary Slang (1990):
bog-standard adj British totally unexceptional, normal and unremarkable. Bog here is used as an otherwise meaningless intensifier.
From Paul Beal, Partridge's Concise Dictionary of Slang and Unconventional English (1989):
bog-standard. Standard, straight from a factory, with no refinement or modification: orig. applied mainly to motorcycles, since mid-1950s; by 1980s > gen. engineering, with wier application. Prob. ex bog-wheel. (Bishop; Hanley, 1988.)
...
bog-wheel. A bicycle: Cambridge undergraduates': earlier C.20. (Keynes, 1981, quoting his diary for 1907.) Its wheels are—like the gap in a water-closet seat—round. Cf. bog n., 1.—2. ["Abbr. bog-house, ... a privy, since early C.19 (in Spy, 1825); orig. Oxford University s{tudents}"; "Abbr. bog-wheel, a bicycle: Marlborough College"] Hence, a motorcycle: Army: WW2. (L.S. Beale.)
So Oxford University students were calling privies "bog-houses" by 1825, and Marlborough College and Cambridge University students were calling bicycles "bog-wheels" by 1907—presumably because of a perceived similarity between the roundness of bicycle wheels and the roundness of the open space in a privy seat. From bicycles, the term bog-wheel was extended to motorcycles, and by World War 2 the term was sometimes shortened (when used in that sense) to the word bog.
The compound adjective bog-standard then arose in the 1950s in the sense of "standard-issue," first in connection with motorcycles, but later applied to other machinery, and eventually (it seems) to such general things as scoops of ice cream.
Probably most British speakers of English would be familiar with the phrase; I have often heard it in the London area, and never thought about its origin. OED mentions the theories about the origin of the phrase given above, then says "The most commonly held view is that the transition from box to bog resulted from a mishearing or misunderstanding of box-standard n." That theory does have the problem that the earliest printed evidence for 'box-standard' is 20 years later than 'bog-standard,' and all the theories about its origin seem a little speculative.
There is a common backronym for bog-standard: "British Or German Standard" - but as the answers above make clear that is very much post hoc.
The phrase caused political controversy in 2001 when the UK Prime Minister's spokesman referred to "bog-standard comprehensive" schools - which was taken to be insulting by some (an interpretation strongly denied by the PM's office.)