Efforts to advance Brexit are “under attack”, Lord Lamont has said, warning peers not to try and make more changes to a bill on triggering Article 50.
The ex-Tory chancellor said calls for a “meaningful vote” on the final deal were “cover” for not wanting to leave.
Peers will debate the issue on Tuesday, having already backed a guarantee of the rights of EU residents to remain.
The Lords must “see sense” and allow Theresa May to begin official talks as soon as possible, Lord Lamont said.
The prime minister wants to notify the EU of the UK’s intention to leave by the end of March but needs the approval of Parliament to do so.
The House of Commons has approved legislation which would kick-start the two-year process, but the Lords has already amended the bill and Labour, Lib Dem and crossbench peers are seeking further changes when debate resumes.
Ministers have given verbal assurances that Parliament will have a vote on the terms of the UK’s exit before the final package is considered by the European Parliament.
Were MPs or peers to reject a deal agreed with the other 27 states, the government has said the UK would still leave, albeit without any formal arrangements.
But critics are concerned what will happen if there is no deal to vote on, something the government has said is unlikely but possible, and they want Parliament to have the authority to send ministers back to the negotiating table to secure better terms.