Private security firms have criticised the UK government for "dithering" over the introduction of tighter rules.
War on Want protestors picketed the security firms' conference
The firms, who employ mercenaries worldwide, say stricter rules will help weed out "rogue" companies and boost the image of respectable ones.
The British Association of Private Security Companies (BAPSC) says guidance was promised in 2002 - but so far nothing has happened.
A BAPSC source said the government was dodging a difficult political decision.
At the BAPSC's annual conference on Tuesday, the association's director general Andrew Bearpark accused the UK government of "dithering" and said it should "get on with it."
"We will work with you, come what may," he said.
Publicly, the security firms - who employ around 10,000 contractors in global hot-spots like Iraq and Afghanistan - are anxious not to be seen to antagonise the government by criticising them too directly.
In private, however, they are furious that the rules of engagement, first promised in a government paper five years ago, have still not been drawn up. It is understood a decision to publish them is currently stalled at ministerial level.
A BAPSC source said: "The government are dodging the decision because it is too difficult and unpopular a subject - it's not a priority for them."
In the meantime, the firms are left to regulate themselves - and vulnerable to attacks from groups such as War On Want. On Monday the charity published a report demanding that the government bring in a total ban on mercenaries in combat.
Criticism of security firms - both American and British - has escalated following incidents such as one last September, when 14 people were killed by guards working for the US-based Blackwater company in Baghdad.
The circumstances of those deaths are being investigated by the US Congress.
The BAPSC favours a mixture of self regulation and government involvement: such as an official investigating ombudsman who would resolve disputes between a private security firm and the host country.
More than anything else, the association craves the official blessing that government regulations would bring.
Mr Bearpark said: "The industry is expanding, and the number of countries where the British government may want to work with our companies is expanding as well.
"For the Ministry of Defence to work with private companies, it has to feel comfortable that it is working with reputable ones."
Dozens of representatives from British private security companies attended BAPSC's second annual conference. The Association was formed last year in "to raise the standards of operation of its members and this emergent industry".
The conference, held at the Royal Geographical Society in Kensington, was picketed by members of War on Want dressed in mercenary costumes.
The charity's campaign director, John Hilary, also criticised the government for not bringing in rules to control security firms.
He said: "We have been working with civil servants to try and bring in these rules - it's been five years since the government brought in a Green Paper calling for regulation, and we have seen no progress at all."
A Foreign Office spokesman confirmed that the decision to publish rules to regulate the behaviour of private security firms was currently being looked at by ministers, but no date has yet been set.
"It is not that we are stalling," said a spokesman. "It is a very difficult area and the government wants to get it right."