U.K. Prime Minister Theresa May is fighting back against Brexit rebels in her ruling Conservative Party as she steps up her battle to start the formal process of pulling Britain out of the European Union. The premier fired government adviser Michael Heseltine after he led a 13-strong revolt in the House of Lords, helping to inflict a second Brexit-bill defeat on May in a vote on Tuesday. The upper chamber rewrote May’s draft law to guarantee Parliament a “meaningful vote” on the outcome of exit talks, potentially vetoing any final agreement and stopping the premier walking away without a deal. May’s team insisted they would seek to delete the changes made by unelected members of the upper house when the bill returns to the House of Commons, probably next week. “I have just been told by the chief whip in the Lords that No. 10 is to sack me from the five jobs with which I have been helping the Government,” Heseltine told the Press Association after the latest vote. “I’m sorry that the expertise which I have put at the Government’s disposal over the last six years has now come to an end. However, in the last resort, I believe, as I said in the House of Lords, the future of this country is inextricably interwoven with our European friends.” After completing its scrutiny in the unelected upper house on Tuesday, the European Union (Notification of Withdrawal) Bill will return to the lower House of Commons where lawmakers will decide whether to accept or reject the Lords’ amendments, probably next Monday. The focus now switches to identifying how many Conservative rebels in the Commons will be prepared to defy the premier and vote to keep the amendments. Seven Tories voted against May on the bill in the Commons last month and former minister Bob Neill told the BBC on Sunday he might vote to keep the Lords amendment guaranteeing Parliament a binding vote. May only has a majority of 17 in the House of Commons, so it needs just a few of her own lawmakers to change sides to make defeat possible. ‘Disappointing’ Defeat Brexit Secretary David Davis said the Lords defeat was “disappointing” and vowed to try to overturn it in the Commons to give May a free hand in negotiations between Britain and the EU.  “It is clear that some in the Lords would seek to frustrate that process, and it is the government’s intention to ensure that does not happen,” he said in a statement. “We will now aim to overturn these amendments in the House of Commons.” The House of Lords voted by 366 to 268 on Tuesday in favor of changing May’s draft legislation to give Parliament the power to send her back to the negotiating table if lawmakers decide the terms of the U.K.’s exit agreement aren’t good enough. It would also stop May walking away from talks without a deal, something she’s threatened to do if she doesn’t like the EU’s offer. Another change to the wording, passed last week, aims to protect the rights of EU citizens living in Britain. May’s team argued the changes would weaken her in negotiations. Brexit Minister George Bridges suggested some opponents of Brexit could use the latest amendment to try to keep Britain in the EU. “This amendment simply makes the negotiations much harder from day one for the prime minister,” he told the House of Lords. “It increases the incentive for the European Union to offer nothing but a bad deal.” May wants the 137-word draft to go through Parliament without changes to give her the maximum freedom to negotiate with EU leaders. Her spokesman, James Slack, told reporters on Tuesday that the premier is “absolutely” on course to meet her own deadline of triggering Brexit negotiations under Article 50 by the end of March. May hasn’t named a date for making the move and there are conflicting reports on when she might pull the trigger, ranging from March 15 to March 31.