The Prime Minister has been accused of acting like "a travelling salesman for the arms industry" as he begins a visit to Gulf states aimed at selling British-made jets.
Speaking to the Daily Telegraph as he arrived in Dubai as part of a three-day tour of the Gulf and the Middle East, David Cameron said: "We do believe countries have a right to defend themselves.
"And we do believe Britain has important defence industries that employ over 300,000 people and so that sort of business is completely legitimate and right."
Cameron has been open about his desire to sell arms to the Saudis, the UAE and Oman.
But anti-arms campaigners have taken aim at the prime minister for the deals done with states that routinely abuse human rights.
British arms have been in the centre of some of the bloodiest conflicts of the last few years, with weapons exported to Libya under Colonel Gaddafi and to Bahrain, where the government responded with extreme violence against anti-regime demonstrators.
Amnesty International UK’s Head of Policy and Government Affairs Allan Hogarth said: "Selling arms to countries like Saudi Arabia and UAE should only be considered if there are absolutely watertight guarantees over them not being used to commit human rights violations.
"Saudi Arabia has been the recipient of record-breaking arms deals involving the UK, yet these have been highly secretive and there’s been little or no follow-up over how the weaponry was used.
"For example, in 2009 the Saudi air force used UK-supplied Tornado fighter-bombers in attacks in Yemen which killed hundreds - possibly thousands - of civilians.
"In one attack conducted by Saudi forces on the town of al-Nadir in November 2009, so many were killed in just one extended family that witnesses say the family ‘had to create a cemetery for themselves’.
"More than two years ago we called for the UK government to urgently investigate Saudi Arabia’s involvement in this episode and meanwhile suspend any further arms supplies to Saudi Arabia.
"In the past a large Saudi chequebook has apparently meant it could purchase weapons as well as silence over its own dreadful human rights record. It’s time for David Cameron to end this deeply disturbing trade-off."
Green MP Caroline Lucas told the Daily Mirror the arms trade was “dirty money”.
"Unfortunately the UK has a shameful track record of exporting arms and equipment to regimes in countries such as Saudi Arabia, Bahrain and Libya – we can’t now claim to be on the side of peace and democracy while our Prime Minister acts as a travelling salesman for the arms industry.
"It’s time to urgently review our role in the international arms trade. Our economy may need a boost, but we certainly don’t need this dirty money.”
Henry McLaughlin, from the Campaign Against Arms Trade, told the paper: "The Prime Minister claims that he wishes to support democracy in the Middle East but at the same time sells arms to these authoritarian regimes.
"Despite everything that has happened in the last two years, the UK government continues to bolster authoritarian regimes with weapons sales and to spend taxpayers’ money on promoting further deals.
"They don’t just approve arms sales, they promote it."
Cameron is keen to restore the best of relations with Gulf states, who are unhappy with the UK's support for Arab Spring uprisings elsewhere in the region with reports that it could lead to British firms being snubbed for future contracts.
But Cameron claimed he was comfortable discussing human rights abuses in countries like Saudi Arabia: "On human rights, there are no no-go areas in this relationship.
"We discuss all of these things but we also show respect and friendship to a very old ally and partner.
"We have one of the strictest regimes anywhere in the world for sales of defence equipment but we do believe that countries have a right to self-defence and we do believe that Britain has important defence industries that employ over 300,000 people so that sort of business is completely legitimate and right.
"We are also partners in defence and security, we worked together in Libya and Afghanistan and we will be talking about all the key regional and global issues."
Britain is also keen to deepen ties with Gulf states amid growing concern about Iran's alleged attempts to develop their own nuclear weapons.
Cameron will hold talks with the Crown Prince of Abu Dhabi and the UAE's Prime Minister about how best to deepen the two countries' military ties, and attempt to persuade the United Arab Emirates to buy 60 of BAE's Typhoon jets in a deal reported to be worth upwards of £3bn.
He will travel to Saudi Arabia on Tuesday - Britain's biggest trading partner in the region - which is also considering adding to its fleet of the aircraft.