LONDON - British Prime Minister Gordon Brown voiced confidence on Thursday that negotiations on the European Union treaty will satisfy British demands but held out the threat of a veto if they did not.

British lawmakers, however, raised concerns about recent changes to the draft text of the treaty, saying they could limit Britain's freedom to choose which areas of EU police and judicial cooperation it wanted to take part in.

Brown said he had to be absolutely sure British national interests were safeguarded in negotiations on the treaty that are due to wrap up at an EU summit in Lisbon next week.

"When we look at the detail of the text and study it I believe that we have succeeded in our negotiating objectives," Brown told a news conference after talks with European Commission President Jose Manuel Barroso.

If Britain did not achieve its demands, "we could not accept the amending treaty. I made that absolutely clear," Brown said.

Brown, who replaced Tony Blair as prime minister in June, is under strong pressure to give British voters a referendum on the treaty from opposition Conservatives, newspapers and some members of his own Labour Party.

Blair offered voters a referendum on the old EU constitution, rejected by French and Dutch voters in 2005. But Brown argues the new treaty is far less ambitious.

Blair negotiated special treatment for Britain on a number of issues, including an exemption from the legal force of a Charter of Fundamental Rights. Britain and Ireland also won the right to choose when they wished to take part in common EU decisions on police and judicial cooperation.

Michael Connarty, chairman of the British parliament's European Scrutiny Committee, wrote to Foreign Secretary David Miliband on Thursday raising the committee's concern over new provisions recently added to the treaty.

Connarty, a member of Brown's Labour Party, said these appeared designed to dissuade Britain or Ireland from exercising a right to stay out of police or judicial cooperation.

Brown appeared to back away from a suggestion early this week that a referendum might be held if Britain's demands were not met. Barroso said he believed Britain's opt-outs would be kept in the text.

The Conservatives' Europe spokesman Mark Francois said Britain's "red lines" were collapsing under detailed scrutiny and that British voters must be allowed their say.

The treaty provides for a long-term EU president, a stronger foreign policy chief and a more democratic voting system.