LONDON (AP) — British Prime Minister Tony Blair defended a decision to halt the investigation of a multi-billion dollar arms deal between BAE Systems PLC and Saudi Arabia, saying last week he took full responsibility for the controversial move.BAE’s shares soared almost seven percent on Friday, adding almost $900 million ($1.8 billion) to its market value.

Blair said advising the Serious Fraud Office to drop its long-running bribery probe was necessary to ensure national security, but lawmakers from throughout the political spectrum — including his own Labour Party — accused him of bowing to Saudi demands.

“Our relationship with Saudi Arabia is vitally important for our country, in terms of counter-terrorism, in terms of the broader Middle East, in terms of helping in respect of Israel/Palestine, and that strategic interest comes first,” Blair told reporters at a European Union summit in Brussels.

“Particularly in circumstances where if this prosecution had gone forward there would have been months and possibly years of ill feeling between us and a key partner and ally, and probably to no purpose,” he said. “I take full responsibility for the advice I gave.”

The SFO was investigating allegations that BAE ran a $60 million ($110 million) “slush fund” offering sweeteners to officials from Saudi Arabia in return for lucrative contracts as part of the Al-Yamamah arms deal in the 1980s.

Al-Yamamah, meaning “the dove”, was the name given to an agreement under which BAE supplied Tornado fighter jets and other military equipment to Saudi Arabia, which paid the British government with barrels of oil. The full extent of the deal was never revealed but it was widely believed to be Britain’s largest-ever export agreement. The British government sold its majority BAE stake in 1981 when it became a public limited company. Reports earlier this month said that the Saudi government had told Britain to drop the probe or lose a $10 billion ($19.6 million) contract to buy Typhoon Eurofighter jets, a deal that will supersede the Al-Yamamah agreement. “We appear to be giving businessmen carte blanche to do business with Saudi Arabia which may involve illegal payments or illegal inducements,” said Eric Illsley, a member of Blair’s own Labour Party who sits on the Foreign Affairs Select Committee. “We have been leaned on very heavily by the Saudis,” Illsley added when asked about possible blackmail in the decision. Liberal Democrat Leader Menzies Campbell said the government should reveal details of advice it received from its legal advisers and conversations between Blair and his Cabinet ministers before the decision was announced last week by Lord Goldsmith, the government’s chief legal adviser.

“If the government does not come completely clean about how, when and why this decision was reached, it will be impossible to resist the conclusion that political and diplomatic pressure has carried more weight than a proper legal assessment,” Campbell said.