The Commons Speaker incurred the private wrath of senior MPs today after warning that it would be a "catastrophic mistake" to water down expenses reforms.

John Bercow surprised MPs with a warning that proposals including a ban on employing spouses and an end to taxpayer-funded mortgages should be implemented in full. One reminded him that he was "servant not master of the House".

Mr Bercow spoke amid speculation that Sir Ian Kennedy, chairman of the Independent Parliamentary Standards Authority, may stop short of pushing through all the recommendations of Sir Christopher Kelly, the standards watchdog. He is thought to have particular concerns over the proposed ban on employing family members, which he thinks might not survive a legal challenge.

In an interview with BBC1’s Andrew Marr Show, Mr Bercow said that "denial, delay or dilution is simply not an option" if MPs were to regain public confidence after the expenses scandal.

His intervention appeared to have upset MPs today. One senior figure, who did not want to reveal his identity, nor his party, accused Mr Bercow of "preaching" at the Commons.

He said: "The Speaker should remember that he is the servant, not the master of the House. The traditional role of the Speaker is to speak for the Commons not to preach at the Commons.

"Sir Ian Kennedy has been appointed as the independent overseer of our new arrangements. He should be allowed to get on with the job, independent of every Member, and that includes the Speaker. The Speaker should remember that there is something to be said for silent reflection."

However Mr Bercow said: "Sir Christopher has produced his recommendations. In my view, they are very sensible, they should be embraced, I hope they will be implemented.

"It is fair only to add that the Parliamentary Standards Act requires the Independent Parliamentary Standards Authority to draw up a scheme for implementation and to consult upon it. So of course that is what will happen.

"But if you are asking me do I think the Kelly recommendations are justified, the answer is yes. Should they be embraced? Yes. Is it important for Parliament to bring about decisive, sweeping, fundamental change quickly? The answer is yes."

The Kelly recommendations sparked anger among some MPs who face losing mortgage interest payments on their second homes, as well as a £10,000-a-year communications allowance and a £25-a-night payment for food. Some of the 200 family members who work for MPs have sought legal advice on the viability of a court challenge to the ban on their employment.

But Mr Bercow said that MPs must recognise that the damage done by the expenses scandal had been "seismic" and they must accept "an element of rough justice" in order to restore the reputation of Parliament.

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