The speaker, Michael Martin, has imposed a "gagging order" on the out-going standards commissioner Elizabeth Filkin.

Fearing that the whole system of standards regulation is being fatally undermined, Martin has prevented the commissioner publishing a second letter in where she expands on the "whispering campaign" which she alleges was conducted against her.

He will ask the standards and privileges committee on Thursday to investigate her claims of a dirty tricks campaign to prevent her seeking a second three-year term in office.

Sources close to the Speaker say she has so far failed to reveal the names of the officials she believes were briefing against her.

Calling in the committee is a move designed to end what is becoming an increasingly bitter and embarrassing row which threatens to open up the whole issue of sleaze again. In the past the committee has clashed with Filkin over her investigations into Peter Mandelson and Geoffrey Robinson.

It is now chaired by senior Conservative Sir George Young who is likely to give her a more sympathetic hearing.