The Lords Constitution Committee recommended that UK ministers block the plan - even if there is a Yes vote in September.
The UK Government should "put the rest of the UK's interests first," the committee's chair, Baroness Jay of Paddington, the daughter of former Labour Prime Minister James Callaghan, said.
Earlier this year, the Herald reported that a UK minister had warned that a Yes vote would not necessarily guarantee independence.
The senior figure said that the "status quo" could be maintained if negotiations between the UK and Scottish governments went badly.
In their new report on Scottish independence published yesterday, peers say there is no "legal or constitutional reason" to sign up to the SNP's timetable. They also recommend Scottish politicians be barred from acting on the UK side during independence negotiations.
But Scots MPs should remain at Westminster until independence day, although they could be prevented from voting on issues outside Scotland, adds the report.
Gordon Banks, Shadow Scotland Office Minister, said: "This report from the House of Lords once again confirms that the remainder of the UK would continue as the successor state, meaning that Scotland would have to renegotiate its terms of entry to a number of organisations, including the EU."
SNP MP Angus MacNeil said: "The House of Lords is an undemocratic anachronism stuffed to the gunnels with over 800 unelected peers of the realm who answer to no electors and are there because of privilege or patronage. To be lectured by them about timetables and for democratic processes is something that could only happen in Westminster. ''