Tony Blair is set to intervene in the debate over Lords reform in a move which could scupper the hopes of those backing a largely-elected second chamber.

The prime minister, who is said to have serious concerns about the consequences of a large body of elected peers, will speak out before MPs vote on the options for change on February 4.

"I have no doubt that the prime minister will set out his view at some stage in the not too distant future," said a Downing Street spokesman.

The move comes amid fresh claims of a cabinet rift over the proposals for reform of the second chamber

The lord chancellor has joined forces with senior ministers including John Prescott in pressing the prime minister to back a totally appointed upper house.

Speaking in the Lords last night, Lord Irvine warned against the "parliamentary disaster of hybridity".

"An appointed House, chosen in accordance with criteria that will make it more representative of the nation as a whole, can add real value to the high value that the House of Commons itself brings," he said.

Commons leader Robin Cook appears to be a lone voice in the cabinet in arguing for the majority of peers to be elected.

"He is totally isolated in the cabinet. He is out on a limb of this one," said a senior MP.

Speculation is growing that Blair will use his intervention to back those calling for a totally appointed second chamber.

Such a move, however, would leave the prime minister open to the charge that he is breaking his 2001 election manifesto pledge.

The policy blueprint said Labour would deliver Lords reform to make the second chamber "more representative and democratic".