In many parliaments and other similar assemblies, seating is typically arranged in banks or rows, with each political party or caucus grouped together. The spokesmen for each group will often sit at the front of their group, and are then known as being on the frontbench and are described as frontbenchers. Those sitting behind them are known as backbenchers.
The 11 frontbenchers signed the letter before Christmas and are sending it now as they try to stop Mr Kennedy standing in the forthcoming leadership election.
Mr Cable said he was not threatening to resign but the position of a lot of frontbenchers "would have to be thought through...depending on what happens over the next few days".
Frontbencher Sandra Gidley, who signed the letter, said: "Charles must think hard about whether he has the personal strength to fight the triple demons of the Labour Party, the Conservative Party and the drink problem."
"Michael's position is incredi-bull," one frontbencher said as he laughed at Mr Howard's declaration over the weekend that he would not have voted in favour of the war in the Commons last year had he known there would be no weapons of mass destruction (WMD) in Iraq.
To the astonishment of MPs, who remember the arch-Atlanticist's strong support for George Bush in the run-up to the war, Mr Howard insisted that he still supported the war and was merely objecting to the government's Commons motion which mentioned WMD.
Conservative MPs had braced themselves for a miserable return to Westminster after their poor performance in last week's byelections when the party slumped to third place in both contests.