Royal Navy may be forced to free captured pirates

Ministers were warned last year over legal problems that mean criminal gangs cannot be prosecuted

Internal Foreign Office documents seen by The Independent on Sunday lay bare the behind-the-scenes wrangling that could neuter the UK-led effort against the growing problem of pirates terrorising vessels in one of the busiest shipping lanes in the world.

The collection of memos and briefing notes detail critical problems with Operation Atalanta since it was hurriedly agreed by the European Union last November in response to a series of high-profile pirate attacks around the Horn of Africa.

Although the UK volunteered to lead the EU's first naval mission, officials have consistently warned ministers that its impact could be limited by the inability to prosecute captured pirates, who are therefore freed – potentially to resume their threat to shipping. Authorities say criminals attacked more than 100 ships off Somalia last year, including hijackings with multimillion-dollar ransom demands.

A supertanker carrying two million barrels of oil became the biggest commercial vessel ever hijacked last November. The Sirius Star was eventually released two months later after its owners parachuted a £2m ransom – reduced from £16m – on to the ship.

EU defence ministers admitted last month that they were struggling to break through complicated international legal agreements to establish how to handle pirates taken into custody, where they could be tried, and what laws apply. They accept that court action – perhaps via special arrangements with selected countries in the region – would act as a significant deterrent.

Documents now reveal that British officials warned of the legal problems – and their potential to embarrass ministers who had committed the nation's forces to the headline-grabbing operation – from the start.

As early as last November, a briefing to ministers pointed out that: "The legal difficulties regarding arrest/detention of pirates mean that it is unlikely that pirates will be able to be brought to justice in the courts."

In a further memo, on 3 December, officials advised David Miliband, the Foreign Secretary, to agree to the launch of Atalanta, "despite failure to conclude ... all the legal agreements sought with regional countries on handover of pirate suspects, accepting that this increases operational and reputational risk in the period until these agreements are concluded". The document also said trying pirates in UK courts was "not desirable", but stated that "the default option ... of releasing the pirates on to a Somali beach after destruction of pirate boats/weapons/ equipment is not attractive either in deterrence or presentational terms".

However, given the Government's prominent role in the operation, it was judged that "a decision not to launch the mission would be embarrassing and, even with careful media handling, we could expect heavy criticism".

Kenya is one of four countries favoured as the regional venue for trials, and Britain is thinking of offering to help its legal system cope with the extra work. The Department of Transport is considering new legislation allowing pirates captured abroad to be tried in the UK.

The shadow Foreign Secretary, William Hague, said: "It will make a mockery of British efforts to combat Somali piracy if we have no effective system to deal with those captured by the Royal Navy, and pirates are simply let loose to attack again."