special report

Cameron, Brown's main rival whose party is current leader in opinion polls, said that the UK should take a more holistic approach to dealing with the issue.

"I think we need to end the division between foreign policy and security policy and Home Office policy, bring it all together and think about our national security."

Afghan strategy

Clegg, who enjoyed an unexpected boost in the polls following the first debate, said that strategy in the war in Afghanistan had jeopardised the fight against international terrorism.

Key debate points
  War in Afghanistan
  UK nuclear weapons
  Europe
  Climate change
  Economy
  Immigration

"The problem is that we've done it in a manner where I don't think we've pursued the right strategy, we haven't given the right equipment to our troops, we haven't had proper international coordination on the ground in Afghanistan."

The leaders also disagreed over the future of the UK's nuclear weapons, which Labour and the Conservatives want to keep, but the Liberal Democrats want to replace with a cheaper alternative.

"I don't think it's right to do what Gordon Brown and David Cameron want which is
now to commit before even making a decision, to spend up to 100 billion pounds renewing in exactly the same old way the Trident nuclear missile system," Clegg said.