Gordon Brown’s attempt to clean up politics after the MPs’ expenses row faces the serious risk of being delayed and, at worst, undermined, by the House of Lords.

The Parliamentary Standards Bill, setting up an independent regulator in place of self-regulation, was amended substantially in the Commons last week and faces a rough ride in the Lords today.

The opposition front benches in the Lords are committed by their party leaders to deliver a Bill by July 21, when the summer recess starts. But this does bind them to the current Bill, allowing scope for amendments.

Backbench peers of all parties are in a rebellious mood, with the old and the bold of the ex-MP lords rumbling angrily about an affront to Parliament’s rights.

Their lordships need to be careful not to overplay their hand. Mr Brown and the party leaders are correct that the public want tough action and that the previous cosy and permissive world of self-regulation has to go. Nor should peers be self-righteous. Two have been suspended over the “cash for amendments” affair and two more are under criminal investigation.

The present system of allowances is defective and open to abuse. Peers have been lucky that most public attention has been on the Commons.

But ministers are at fault for rushing the Bill through. The Lords Constitution Committee has issued two powerful reports warning against fast-track procedures, especially on a Bill that has big constitutional implications. The committee has rejected the acceleration of the usual timetable for debating the measure, and has also insisted on safeguards.

Jack Straw, the Lord Chancellor, was meeting opposition parties last night to discuss proposals for a sunset clause, under which the Bill’s provisions would expire after a certain date unless renewed or replaced by fresh legislation. A one-year limit was defeated by MPs, but a two-year limit looks likely.

The main concern is over infringing Parliament’s traditional freedoms under the 1689 Bill of Rights. Some of these points were addressed in the Commons, both through amendment and defeat (although MPs made it harder to prosecute members for paid advocacy by voting that their proceedings cannot be cited in court).

Peers will press for a more formal recognition that nothing in the new measure will override the Bill of Rights. They will also urge that the new regulator should report only to Parliament, not recommend sanctions, leaving disciplinary decisions to MPs and preventing court challenges.

Backbench peers could back an amendment today insisting on the usual two-week interval between a second reading and committee stage. This would wreck the frontbench deal by preventing the Bill becoming law before the recess. The Government should pre-empt such a row by announcing that Parliament will give up two weeks of its recess to come back in September, signalling both self-sacrifice and seriousness. In their current indignation, however, peers should not ignore public anger about politicians’ behaviour. Both MPs and peers need to show that Parliament is capable of cleaning itself up. That is now in doubt.

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