Gordon Brown gave notice last night that the purge of Labour MPs considered to have broken rules on expenses could be wider than expected.

On the day Labour set up a new “star chamber” with the power to kick out MPs guilty of claiming too much, Mr Brown suggested that backing from an MP’s constituency party would not necessarily be enough to save them.

He raised new questions over the future of Margaret Moran, describing the whip’s expenses claims as “completely unacceptable”. The Luton South MP is already under investigation after spending £22,000 to pay for dry-rot treatment at her partner’s home in Southampton.

She has agreed to repay the money and has been backed by her local party. But Mr Brown said any Labour MP found to have “defied the rules” will not be allowed to stand at the next election. Mr Brown said an internal party investigation was under way into the Luton South MP, adding: “The question will be debated by us as a party.”

The TV presenter Esther Rantzen is threatening to stand against Ms Moran at the next general election as an anti-sleaze candidate.

Mr Brown also sharply criticised his Cabinet colleague Hazel Blears, who has admitted avoiding capital gains tax through “flipping” homes designations. She has agreed to repay £13,332 after making a profit from selling a flat repaired with taxpayers’ money.

Mr Brown called her expenses claims “totally unacceptable behaviour” before adding: “Hazel Blears has paid the money back. But she has not broken the law, she has not broken the rules of the House of Commons.”

Ms Blears looks safe for now, but her Cabinet future is uncertain.

Two Labour MPs have been suspended for claiming for mortgage interest payments after their mortgages were paid off.

Some ministers have also faced questions about their expenses claims.

Earlier in the day the NEC endorsed a “tough new disciplinary process” to prevent MPs who had broken the rules from standing for parliament as Labour candidates.

Its “star chamber” panel will interview MPs who were the subject of allegations. It will have the power to recommend that MPs should not stand for under the Labour banner.

Later in the day the Speaker announced a “robust” set of new restrictions on MPs expenses agreed at the meeting of party leaders to take immediate effect.

They included a ban on claiming the second-home allowance for furniture, household goods, gardening and cleaning, and a £1,250-a-month cap on mortgage interest payments.

The practice of switching the designation of main and second homes — known as “flipping” — will also be banned for the rest of 2009-10 unless there are exceptional circumstances.

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