British Prime Minister David Cameron ruled out a head-to-head televised debate with the opposition Labor leader ahead of the May 7 election, sidestepping a potentially risky clash with Ed Miliband but drawing accusations of cowardice from rivals.
While the Conservatives and Labor are neck and neck in the polls, Miliband has the most to gain from a head-to-head debate as his personal ratings are far lower than Cameron's.
A letter from Cameron's office said he would only take part in one debate and that it must include leaders from minor political parties, rejecting broadcasters' proposals to hold several debates, including a one-on-one debate with Miliband.
"There should be one 90 minute debate between seven party leaders," the letter said.
It proposed including the anti-European Union party UKIP, Scottish and Welsh nationalists, the Green party and the junior coalition partner Liberal Democrats.
"This is our final offer, and to be clear... the Prime Minister will not be participating in more than one debate," the letter said.
In 2010, 22 million people watched Britain's first U.S.-style televised election debates: Three three-way contests between Cameron, the then incumbent Labor Prime Minister Gordon Brown and Liberal Democrat leader Nick Clegg.
A strong performance at those debates by Clegg saw his party rise in the opinion polls, and they have since been cited as a factor that cost Cameron an outright election victory and forced him to form a coalition government with the Liberal Democrats.
Thursday's intervention is the latest in a long-running spat between Cameron, rival political parties and broadcasters over the timing and format of the debates.
Cameron's ultimatum drew sharp criticism from opponents.
"This is an outrageous attempt from the Prime Minister to bully the broadcasters into dropping their proposals for a head-to-head debate," Labor's election strategy chief Douglas Alexander said.
Clegg said Cameron should stop holding the British public to ransom by trying to dictate terms, while a spokesman for the UK Independence Party (UKIP), said Cameron was "acting chicken."
The row comes as opinion polling in Scotland showed the crucial role that so-called minor parties are likely to play at the ballot, highlighting a surge in nationalism that could see the Scottish National Party inflict heavy losses on Labor.
Surveys commissioned by Michael Ashcroft, the former deputy chairman Cameron's Conservative Party, showed swings of between 20 percent and 28.5 percent to the Scottish National Party (SNP). The poll showed labor could lose their safest seat in Scotland, that of retiring former prime minister Gordon Brown.