The basic unrefined article.
First recorded in the early 1960s, although there are numerous hearsay reports of its colloquial use in the UK before then. Given that it is quite a colourful-sounding phrase and that it is quite recent, it is surprising that a definitive origin can't be found. Most of the early citations - and there aren't many of those - come from the technical world, either computing or engineering. The earliest found to date is from the October 1968 edition of Hot Car:
The brakes are bog-standard - anyway Barry says he only uses them in the paddock!
The lack of early citations indicates that the phrase toddled along as slang for some time before anyone took much notice of it. Its use by Alistair Campbell, who was until 2003 Tony Blair's Director of Communications and Strategy (a.k.a. spin doctor), brought it to public attention in the UK. In February 2001 Campbell, who has a reputation as a confrontational and macho speaker, said:
"The day of the bog-standard comprehensive school is over."
Comprehensives are UK mixed-ability secondary schools. The comment was clearly intended to paint the schools in a poor light and indicate the New Labour administration's negative opinion of them.
But why 'bog standard'? It may result from the association with the word 'bog', which has long been used in the UK to mean toilet. Indeed, that meaning is used in one of the more ingenious derivations that correspondents have suggested - that it was coined in the BBC as a derogatory description of the production values of their rival ATV, an organisation run by Lew Grade. The linguistic progression is supposed to go Lew Grade -> loo grade -> toilet quality -> bog standard. A neat construction, but most likely a back-formation and, hearsay apart, there's no evidence to support it.
The other most often repeated theory of the derivation is that it is a mispronunciation of 'box standard', the term referring to unmodified goods coming straight from the box. This appears to be a later expression, first recorded in 1983, but is likely to have been around in everyday speech for some years prior to that. If one phrase did influence the other, it is more likely that 'box-standard' is a mispronounced or euphemistic version of 'bog standard'. In the February 1983 edition of Computerworld magazine we have a comment from Sir Clive Sinclair, the inventor and entrepreneur:
"We cannot foresee a day when a computer becomes just a standard box. There will be box-standard machines along the road, but we do not simply have to make those. There will always be something fresh waiting to be done."
Again, as with 'bog standard', there are few early citations. Here's another from Richard Cooke's 1991 book Paintball: The Combat Adventure Sport:
"An inspection of the hammer reveals one of the most hi-tech items currently fitted to a box standard weapon."
We may find evidence to link 'bog standard' to some specific event or process, but somehow I doubt it. Like the American phrase 'brown bag', it seems that 'bog standard' is just an evocative phrase meaning basic/ordinary/unrefined.
We may not be able to pin down the phrase's origin but what we can do is refute a story that was broadcast in the BBC's quiz show QI in November 2005. The researchers for the show put into the mouth of the normally erudite and knowledgeable Stephen Fry the notion that early construction sets were labelled 'box standard' and 'box deluxe':
Fry: In the early years of the 20th century, children's construction sets, like Meccano, were sold in two kinds, labelled "Box Standard" and "Box Deluxe". And that, or so they say and persuade me, is where we get the two phrases "bog standard" and "dog's bollocks"!
Neither of these two ideas holds water. The suggestion that 'bog standard' comes from 'box standard' is plausible enough but, as we have seen, lacks any supporting evidence. The notion that 'the dog's bollocks' comes from 'box deluxe' is pure invention; even if they could come up with such a box label, and that remains noticeably lacking, how is that linguistic jump supposed to have occurred, and why the long gap between the construction sets and the phrase being found in print?
Fry did at least seem to have less than 100% faith in the story and qualified it with etymology's most telling weasel words "or so they say...".