Story highlights Theresa May becomes first Prime Minister to sit in House of Lords for debate in memory

A record 191 members of Parliament's upper house have lined up to speak on Brexit bill

London (CNN) Unfettered by the concerns of voters, the UK's unelected House of Lords has begun its second day of debate on the "key purpose and principles" of legislation to withdraw from the European Union.

A record 191 members of Parliament's upper house have lined up to speak in what is likely to be the largest second reading debate in the chamber's history.

No one expects the peers to block the UK's departure from the 27-nation EU, but they could vote at the committee stage to accept amendments to the bill. The legislation would have to go back to the House of Commons if the House of Lords adds amendments, which would delay the bill's passage, endangering Downing Street's March 31 deadline to trigger the Brexit process.

For the first time in living memory, a British Prime Minister was present during a House of Lords debate.

On Monday, Prime Minister Theresa May sat on the steps in front of the royal throne, a position she is entitled to occupy as a member of the Queen's Privy Council , a group of advisers to the monarchy that includes present or former members of the House of Commons or House of Lords.

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