The Afghan security forces are "thoroughly in control" of counter-insurgency, said Brigadier Ben Barry, senior fellow on land warfare at the International Institute for Strategic Studies (IISS).
They should be able to successfully protect the April 5 presidential election, though with 11 candidates, it is difficult to predict whether the transfer of power will be smooth, he said.
The Taliban's military offencive in 2013 failed, while their attacks in Kabul had political but negligible security impact, Barry said.
He said government forces were holding the military gains made by the NATO troop surge and their ability to retain control would continue to improve.
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"The most likely security situation after complete transition on January 1, 2015 is a situation very much like today," he said.
The British brigadier, who commanded NATO troops in Bosnia, said the alliance was "very worried" about Afghan President Hamid Karzai's refusal to sign the bilateral security agreement.
"That, in the long term, is a considerable risk to Afghanistan's security and stability," he said.
He said the Taliban's recent actions showed they were "believing their own propaganda".
"There is evidence from recent Taliban behaviour that they are living in a fantasy world," he said.
"It's going to be very difficult to completely eradicate the Taliban, the narcotics trade and corruption," he added.
"But I think the chances of the Taliban achieving their aims militarily next year are very, very low.