The EU Withdrawal Bill will be subject to intense Lords scrutiny in the New Year, with fears Remainers could stall the whole process.
Lord Lisvane warned peers could send the key legislation back to the Commons several times over their concerns.
The vital legislation transfers EU law into British statute, raising fears of sweeping powers being given to the Government without proper scrutiny.
Although the Lords is bound by convention not to block the Commons’ will, both houses have to agree on the legisaltion.
And Lord Lisvane stressed peers had the power to ask commons to “think again” on key Brexit issues.
He said: “If the bill is not further amended, then an area of concern in the Lords is going to be the largely untrammelled powers proposed to be given to ministers.
“If the bill is not further amended, it would represent the largest peacetime transfer of power from parliament to the executive.”
Theresa May suffered her first Commons defeat this month after an amendment giving MPs a meaningful vote on the final deal gained cross-party support.
And Lord Lisvane said peers could have similar success if they chose amendments that would appeal across the political divide.
But he denied the back-and-forth between Houses would be down to “backdoor Remainer stuff”.
He said: “It happens to be in the context of Brexit. But it would be objectionable in any circumstances.”
The House of Lords is thought to have already ramped up the number of days it will be sitting this year as Brexit legislation threatens to clog up day-to-day business.
A number of peers have threatened to cause havoc with the Bill when it does reach the House.
Labour’s Lord Adonis celebrated Theresa May’s Commons defeat, and promised her more trouble to come.
He tweeted: “First step towards defeat of Brexit. And this is before the Lords has got going on the National Betrayal Bill.High-profile Remainer Lord Heseltine has also hit out at the Brexit legislation and said he will act in the “national interest” .
He has even publicly wished for a Labour government if it means Brexit can be stopped.
The Tory peer said: “Parliamentary democracy rests power in parliament and particularly the House of Commons.
“That’s where decisions have to be taken. And, even when they are taken.
“Even when we’ve had Labour governments, with a mandate, people like me in the Conservative party have fought their decisions line by line in the House of Commons.
“Then when they’ve had an election and we’ve won, we’ve changed them. That is what parliament is fully entitled to do.
“The fact that there was a referendum, on a very imprecise issue, is a stepping stone, but the ultimate decision rests with parliament.
“As a parliamentarian myself, anything I’m asked to do, I will do it in the national interest.”