UKIP leader Nigel Farage has insisted he did not "bottle it" by deciding not to run in the by-election to replace MP Patrick Mercer.
Mr Mercer stood down ahead of being banned from Parliament for six months over a "cash-for-questions" scandal.
But Mr Farage said he would not contest the Newark constituency, arguing he would look like an "opportunist".
Tory MP Ben Wallace called him a "chicken", while Labour's Rachel Reeves said he "didn't want to fight".
There had been speculation Mr Farage would be his party's candidate in the Nottinghamshire seat, following Mr Mercer's resignation on Tuesday.
But the UKIP leader announced on Wednesday that he would not be taking part.
Asked to respond to Conservative and Labour claims that he had "bottled it", Mr Farage said his opponents "could say what they like".
"A wise general does not fight every battle, he chooses his battles," he told the BBC. "I am not going to be parachuted into a constituency where I would be seen as opportunist."
Fighting Newark, an area he had no connection with, would be tantamount to "deserting" UKIP activists campaigning to try to come top in the European elections, he said.
He promised UKIP would "throw the kitchen sink" at winning the seat, held by the Conservatives with a majority of 16,152 at the 2010 general election.
Mr Farage said: "I think I have shown some courage over the years. I have helped take this party from nothing into a position where last Sunday it was leading the opinion polls in a national election."
He added: "I'm a fighter. I'm a warrior. But you have to pick your battles in life."
BBC News - UKIP leader Nigel Farage: I didn't bottle by-election
It would also show once and for all that they have no policies and, despite claims from the very vocal minority, in reality they have no substantive support. Less bottle than a can of coke.
Mr Mercer stood down ahead of being banned from Parliament for six months over a "cash-for-questions" scandal.
But Mr Farage said he would not contest the Newark constituency, arguing he would look like an "opportunist".
Tory MP Ben Wallace called him a "chicken", while Labour's Rachel Reeves said he "didn't want to fight".
There had been speculation Mr Farage would be his party's candidate in the Nottinghamshire seat, following Mr Mercer's resignation on Tuesday.
But the UKIP leader announced on Wednesday that he would not be taking part.
Asked to respond to Conservative and Labour claims that he had "bottled it", Mr Farage said his opponents "could say what they like".
"A wise general does not fight every battle, he chooses his battles," he told the BBC. "I am not going to be parachuted into a constituency where I would be seen as opportunist."
Fighting Newark, an area he had no connection with, would be tantamount to "deserting" UKIP activists campaigning to try to come top in the European elections, he said.
He promised UKIP would "throw the kitchen sink" at winning the seat, held by the Conservatives with a majority of 16,152 at the 2010 general election.
Mr Farage said: "I think I have shown some courage over the years. I have helped take this party from nothing into a position where last Sunday it was leading the opinion polls in a national election."
He added: "I'm a fighter. I'm a warrior. But you have to pick your battles in life."
BBC News - UKIP leader Nigel Farage: I didn't bottle by-election
It would also show once and for all that they have no policies and, despite claims from the very vocal minority, in reality they have no substantive support. Less bottle than a can of coke.
Comment