LONDON (Reuters) - British Prime Minister Theresa May has been clear that the legislation needed for her to trigger formal divorce talks with the European Union should be passed by parliament unamended, her spokesman said on Thursday.

Britain's Prime Minister Theresa May holds a press conference with her counterpart from Italy Paolo Gentiloni (not shown) at Number 10 Downing Street in London, February 9, 2017. REUTERS/Toby Melville

Parliament’s upper house inflicted a defeat on the government on Wednesday, voting for a change to her Brexit plan that says she can only trigger Article 50 of the EU’s Lisbon Treaty if she promises to protect the rights of EU citizens living in Britain.

May has said she wants to guarantee EU citizens’ rights and hopes this can be resolved as a priority once the negotiations begin, but she does not want to do so until other member states agreed to a reciprocal deal for Britons abroad.

The government hopes to overturn the changes when the legislation returns to the lower house of parliament, which last month passed the bill with no amendments.

“The prime minister has made clear her intention that the bill should be passed unamended,” her spokesman told reporters.

“MPs (members of the lower house) have already voted it through unamended at the first stage so we expect that to be the case again.”

The upper house, the House of Lords, will debate further possible changes to the legislation on March 7. The bill will then return to the lower house, the House of Commons, most likely in the week of March 13.

The spokesman said the prime minister was committed to her plan to trigger divorce talks by the end of March and said the Lords vote would not have any impact on that.

The opposition Liberal Democrat leader in the Lords agreed.

“This bill will go through, there has never been any question about it going through,” Dick Newby told Sky News.

“I think the Lords collectively will back off,” he said. “The idea that ... this somehow jeopardizes the 31 March deadline is complete baloney.”