First the British government denied renditions ever took place through Diego Garcia, a British territory in the Indian Ocean. Then in 2008 it finally admitted the truth. Now, years later, documents relating to a key period have reportedly been accidentally destroyed when they were soaked in water. Here are seven critical points about the affair.

1. Two rendition flights landed on Diego Garcia in 2002, the year covered by the 'lost' documents



The year the drowned documents apparently covered, 2002, is when the UK government admitted that it saw two CIA torture flights land on the island. There is an undeniable stink of the destruction of evidence here. Why, in none of the many prior discussions between MPs and the government about Diego Garcia over the years, was this "water damage" never once mentioned?

2. It is not only the records for 2002 we need to see



Diego Garcia's role may extend far beyond 2002. None of the flight documents that we know exist – "water damaged" or not – have yet been provided to the public or, apparently, to the MPs who are meant to provide oversight.

3. For years the UK government denied all knowledge

For a long time, ministers claimed that anyone who thought the UK was involved in renditions was a conspiracy theorist. Here's foreign secretary Jack Straw in 2005: "Unless we all start to believe in conspiracy theories and that the officials are lying, that I am lying, that behind this there is some kind of secret state which is in league with some dark forces in the United States, and also let me say, we believe that Secretary Rice is lying, there simply is no truth in the claims that the United Kingdom has been involved in rendition full stop."

Three years later, the then foreign secretary, David Miliband, was forced to confess that this was spectacularly untrue, admitting to parliament that two CIA "rendition" flights carrying detainees had in fact made use of the British territory of Diego Garcia – an atoll in the Indian Ocean – in 2002.

4. Renditions enabled horrific torture beyond the rule of law



Before we become swamped in the euphemisms of the war on terror, it is worth remembering what Bush-era "rendition" really meant. The CIA, with significant support from Britain and other allies, would kidnap people and fly them to countries where they could be tortured. Detainees spent months or years in secret prisons beyond the rule of law. In the dungeons of Gaddafi, Mubarak or Assad they were beaten and hung from the walls, and in some cases had their genitals cut with a scalpel.

5. Among the victims were children and pregnant women



The victims of the rendition programme were not just men; they included women and children. The al-Saadi family was "rendered" en masse to Libya in 2004: Sami, a prominent anti-Gaddafi dissident, his wife Karima and their four children, the eldest 12 and the youngest just six. Fatima Boudchar, the wife of another Gaddafi opponent, was five months' pregnant when she was kidnapped with her husband and flown to Gaddafi's prisons in the same year.

6. Britain played a key role



We now know that a high-ranking MI6 official wrote to Gaddafi's spy chief to congratulate him on the arrival of the "air cargo" – Boudchar and her husband, Abdul Hakim Belhadj. Tony Blair embraced Gaddafi, welcoming him back to "civilised" society, the very same month – March 2004.

Crucially, given revelations that key flight documents – never before released – relating to Diego Garcia have conveniently suffered "water damage", there is evidence that the US sought to make use of the island in the rendition of Belhadj and Boudchar. Despite the emergence of a flight plan showing that the CIA intended to stop off on the British territory, the UK government has repeatedly refused to say whether or not the US asked to send the couple via the island in 2004 and whether it was allowed. The destroyed documents would have shed light on what British officials knew about Diego Garcia's potential use as a secret prison.

7. Political oversight of British involvement has spectacularly failed



Parliament's intelligence and security committee said in 2007 that there was "no evidence that the UK agencies were complicit in any 'extraordinary rendition operations'", adding, "we are satisfied that there is no evidence that US rendition flights have used UK airspace". In the wake of this spectacular failure of accountability, it was felt that something more effective was needed, resulting ultimately in the establishment of an inquiry into UK involvement in rendition and torture by David Cameron in July 2010. The inquiry, he said, would be "led by a judge" and "look at whether Britain was implicated in the improper treatment of detainees".

You would be forgiven for failing to have noticed the inquiry, because it never really happened. At the tail end of last year, as MPs packed up for their Christmas break, the government quietly wound up the detainee inquiry before it could get going. It passed the inquiry's functions to the intelligence and security committee – the same group of MPs that catastrophically failed to do their job in the first place.

So we are, in effect, back where we started. Short of a major change in how we hold the state accountable, it will continue to conveniently lose evidence showing its part in serious abuses, and our political "watchdogs" will continue to be either unable or too useless to do anything about it.